light travel kilometres

What is the speed of light?

The speed of light is the speed limit of the universe. Or is it?

What is a light-year?

• Speed of light FAQs
• Special relativity
• Faster than light
• Slowing down light
• Faster-than-light travel

Bibliography

The speed of light traveling through a vacuum is exactly 299,792,458 meters (983,571,056 feet) per second. That's about 186,282 miles per second — a universal constant known in equations as "c," or light speed. 

According to physicist Albert Einstein 's theory of special relativity , on which much of modern physics is based, nothing in the universe can travel faster than light. The theory states that as matter approaches the speed of light, the matter's mass becomes infinite. That means the speed of light functions as a speed limit on the whole universe . The speed of light is so immutable that, according to the U.S. National Institute of Standards and Technology , it is used to define international standard measurements like the meter (and by extension, the mile, the foot and the inch). Through some crafty equations, it also helps define the kilogram and the temperature unit Kelvin .

But despite the speed of light's reputation as a universal constant, scientists and science fiction writers alike spend time contemplating faster-than-light travel. So far no one's been able to demonstrate a real warp drive, but that hasn't slowed our collective hurtle toward new stories, new inventions and new realms of physics.

Related: Special relativity holds up to a high-energy test

A l ight-year is the distance that light can travel in one year — about 6 trillion miles (10 trillion kilometers). It's one way that astronomers and physicists measure immense distances across our universe.

Light travels from the moon to our eyes in about 1 second, which means the moon is about 1 light-second away. Sunlight takes about 8 minutes to reach our eyes, so the sun is about 8 light minutes away. Light from Alpha Centauri , which is the nearest star system to our own, requires roughly 4.3 years to get here, so Alpha Centauri is 4.3 light-years away.

"To obtain an idea of the size of a light-year, take the circumference of the Earth (24,900 miles), lay it out in a straight line, multiply the length of the line by 7.5 (the corresponding distance is one light-second), then place 31.6 million similar lines end to end," NASA's Glenn Research Center says on its website . "The resulting distance is almost 6 trillion (6,000,000,000,000) miles!"

Stars and other objects beyond our solar system lie anywhere from a few light-years to a few billion light-years away. And everything astronomers "see" in the distant universe is literally history. When astronomers study objects that are far away, they are seeing light that shows the objects as they existed at the time that light left them. 

This principle allows astronomers to see the universe as it looked after the Big Bang , which took place about 13.8 billion years ago. Objects that are 10 billion light-years away from us appear to astronomers as they looked 10 billion years ago — relatively soon after the beginning of the universe — rather than how they appear today.

Related: Why the universe is all history

Speed of light FAQs answered by an expert

We asked Rob Zellem, exoplanet-hunter and staff scientist at NASA's Jet Propulsion Lab, a few frequently asked questions about the speed of light. 

Dr. Rob Zellem is a staff scientist at NASA's Jet Propulsion Laboratory, a federally funded research and development center operated by the California Institute of Technology. Rob is the project lead for Exoplanet Watch, a citizen science project to observe exoplanets, planets outside of our own solar system, with small telescopes. He is also the Science Calibration lead for the Nancy Grace Roman Space Telescope's Coronagraph Instrument, which will directly image exoplanets. 

What is faster than the speed of light?

Nothing! Light is a "universal speed limit" and, according to Einstein's theory of relativity, is the fastest speed in the universe: 300,000 kilometers per second (186,000 miles per second). 

Is the speed of light constant?

The speed of light is a universal constant in a vacuum, like the vacuum of space. However, light *can* slow down slightly when it passes through an absorbing medium, like water (225,000 kilometers per second = 140,000 miles per second) or glass (200,000 kilometers per second = 124,000 miles per second). 

Who discovered the speed of light?

One of the first measurements of the speed of light was by Rømer in 1676 by observing the moons of Jupiter . The speed of light was first measured to high precision in 1879 by the Michelson-Morley Experiment. 

How do we know the speed of light?

Rømer was able to measure the speed of light by observing eclipses of Jupiter's moon Io. When Jupiter was closer to Earth, Rømer noted that eclipses of Io occurred slightly earlier than when Jupiter was farther away. Rømer attributed this effect due the time it takes for light to travel over the longer distance when Jupiter was farther from the Earth. 

How did we learn the speed of light?

As early as the 5th century BC, Greek philosophers like Empedocles and Aristotle disagreed on the nature of light speed. Empedocles proposed that light, whatever it was made of, must travel and therefore, must have a rate of travel. Aristotle wrote a rebuttal of Empedocles' view in his own treatise, On Sense and the Sensible , arguing that light, unlike sound and smell, must be instantaneous. Aristotle was wrong, of course, but it would take hundreds of years for anyone to prove it. 

In the mid 1600s, the Italian astronomer Galileo Galilei stood two people on hills less than a mile apart. Each person held a shielded lantern. One uncovered his lantern; when the other person saw the flash, he uncovered his too. But Galileo's experimental distance wasn't far enough for his participants to record the speed of light. He could only conclude that light traveled at least 10 times faster than sound.

In the 1670s, Danish astronomer Ole Rømer tried to create a reliable timetable for sailors at sea, and according to NASA , accidentally came up with a new best estimate for the speed of light. To create an astronomical clock, he recorded the precise timing of the eclipses of Jupiter's moon , Io, from Earth . Over time, Rømer observed that Io's eclipses often differed from his calculations. He noticed that the eclipses appeared to lag the most when Jupiter and Earth were moving away from one another, showed up ahead of time when the planets were approaching and occurred on schedule when the planets were at their closest or farthest points. This observation demonstrated what we today know as the Doppler effect, the change in frequency of light or sound emitted by a moving object that in the astronomical world manifests as the so-called redshift , the shift towards "redder", longer wavelengths in objects speeding away from us. In a leap of intuition, Rømer determined that light was taking measurable time to travel from Io to Earth. 

Rømer used his observations to estimate the speed of light. Since the size of the solar system and Earth's orbit wasn't yet accurately known, argued a 1998 paper in the American Journal of Physics , he was a bit off. But at last, scientists had a number to work with. Rømer's calculation put the speed of light at about 124,000 miles per second (200,000 km/s).

In 1728, English physicist James Bradley based a new set of calculations on the change in the apparent position of stars caused by Earth's travels around the sun. He estimated the speed of light at 185,000 miles per second (301,000 km/s) — accurate to within about 1% of the real value, according to the American Physical Society .

Two new attempts in the mid-1800s brought the problem back to Earth. French physicist Hippolyte Fizeau set a beam of light on a rapidly rotating toothed wheel, with a mirror set up 5 miles (8 km) away to reflect it back to its source. Varying the speed of the wheel allowed Fizeau to calculate how long it took for the light to travel out of the hole, to the adjacent mirror, and back through the gap. Another French physicist, Leon Foucault, used a rotating mirror rather than a wheel to perform essentially the same experiment. The two independent methods each came within about 1,000 miles per second (1,609 km/s) of the speed of light.

Another scientist who tackled the speed of light mystery was Poland-born Albert A. Michelson, who grew up in California during the state's gold rush period, and honed his interest in physics while attending the U.S. Naval Academy, according to the University of Virginia . In 1879, he attempted to replicate Foucault's method of determining the speed of light, but Michelson increased the distance between mirrors and used extremely high-quality mirrors and lenses. Michelson's result of 186,355 miles per second (299,910 km/s) was accepted as the most accurate measurement of the speed of light for 40 years, until Michelson re-measured it himself. In his second round of experiments, Michelson flashed lights between two mountain tops with carefully measured distances to get a more precise estimate. And in his third attempt just before his death in 1931, according to the Smithsonian's Air and Space magazine, he built a mile-long depressurized tube of corrugated steel pipe. The pipe simulated a near-vacuum that would remove any effect of air on light speed for an even finer measurement, which in the end was just slightly lower than the accepted value of the speed of light today. 

Michelson also studied the nature of light itself, wrote astrophysicist Ethan Siegal in the Forbes science blog, Starts With a Bang . The best minds in physics at the time of Michelson's experiments were divided: Was light a wave or a particle? 

Michelson, along with his colleague Edward Morley, worked under the assumption that light moved as a wave, just like sound. And just as sound needs particles to move, Michelson and Morley and other physicists of the time reasoned, light must have some kind of medium to move through. This invisible, undetectable stuff was called the "luminiferous aether" (also known as "ether"). 

Though Michelson and Morley built a sophisticated interferometer (a very basic version of the instrument used today in LIGO facilities), Michelson could not find evidence of any kind of luminiferous aether whatsoever. Light, he determined, can and does travel through a vacuum.

"The experiment — and Michelson's body of work — was so revolutionary that he became the only person in history to have won a Nobel Prize for a very precise non-discovery of anything," Siegal wrote. "The experiment itself may have been a complete failure, but what we learned from it was a greater boon to humanity and our understanding of the universe than any success would have been!"

Special relativity and the speed of light

Einstein's theory of special relativity unified energy, matter and the speed of light in a famous equation: E = mc^2. The equation describes the relationship between mass and energy — small amounts of mass (m) contain, or are made up of, an inherently enormous amount of energy (E). (That's what makes nuclear bombs so powerful: They're converting mass into blasts of energy.) Because energy is equal to mass times the speed of light squared, the speed of light serves as a conversion factor, explaining exactly how much energy must be within matter. And because the speed of light is such a huge number, even small amounts of mass must equate to vast quantities of energy.

In order to accurately describe the universe, Einstein's elegant equation requires the speed of light to be an immutable constant. Einstein asserted that light moved through a vacuum, not any kind of luminiferous aether, and in such a way that it moved at the same speed no matter the speed of the observer. 

Think of it like this: Observers sitting on a train could look at a train moving along a parallel track and think of its relative movement to themselves as zero. But observers moving nearly the speed of light would still perceive light as moving away from them at more than 670 million mph. (That's because moving really, really fast is one of the only confirmed methods of time travel — time actually slows down for those observers, who will age slower and perceive fewer moments than an observer moving slowly.)

In other words, Einstein proposed that the speed of light doesn't vary with the time or place that you measure it, or how fast you yourself are moving. 

Therefore, objects with mass cannot ever reach the speed of light. If an object ever did reach the speed of light, its mass would become infinite. And as a result, the energy required to move the object would also become infinite: an impossibility.

That means if we base our understanding of physics on special relativity (which most modern physicists do), the speed of light is the immutable speed limit of our universe — the fastest that anything can travel. 

What goes faster than the speed of light?

Although the speed of light is often referred to as the universe's speed limit, the universe actually expands even faster. The universe expands at a little more than 42 miles (68 kilometers) per second for each megaparsec of distance from the observer, wrote astrophysicist Paul Sutter in a previous article for Space.com . (A megaparsec is 3.26 million light-years — a really long way.) 

In other words, a galaxy 1 megaparsec away appears to be traveling away from the Milky Way at a speed of 42 miles per second (68 km/s), while a galaxy two megaparsecs away recedes at nearly 86 miles per second (136 km/s), and so on. 

"At some point, at some obscene distance, the speed tips over the scales and exceeds the speed of light, all from the natural, regular expansion of space," Sutter explained. "It seems like it should be illegal, doesn't it?"

Special relativity provides an absolute speed limit within the universe, according to Sutter, but Einstein's 1915 theory regarding general relativity allows different behavior when the physics you're examining are no longer "local."

"A galaxy on the far side of the universe? That's the domain of general relativity, and general relativity says: Who cares! That galaxy can have any speed it wants, as long as it stays way far away, and not up next to your face," Sutter wrote. "Special relativity doesn't care about the speed — superluminal or otherwise — of a distant galaxy. And neither should you."

Does light ever slow down?

Light in a vacuum is generally held to travel at an absolute speed, but light traveling through any material can be slowed down. The amount that a material slows down light is called its refractive index. Light bends when coming into contact with particles, which results in a decrease in speed.

For example, light traveling through Earth's atmosphere moves almost as fast as light in a vacuum, slowing down by just three ten-thousandths of the speed of light. But light passing through a diamond slows to less than half its typical speed, PBS NOVA reported. Even so, it travels through the gem at over 277 million mph (almost 124,000 km/s) — enough to make a difference, but still incredibly fast.

Light can be trapped — and even stopped — inside ultra-cold clouds of atoms, according to a 2001 study published in the journal Nature . More recently, a 2018 study published in the journal Physical Review Letters proposed a new way to stop light in its tracks at "exceptional points," or places where two separate light emissions intersect and merge into one.

Researchers have also tried to slow down light even when it's traveling through a vacuum. A team of Scottish scientists successfully slowed down a single photon, or particle of light, even as it moved through a vacuum, as described in their 2015 study published in the journal Science . In their measurements, the difference between the slowed photon and a "regular" photon was just a few millionths of a meter, but it demonstrated that light in a vacuum can be slower than the official speed of light. 

Can we travel faster than light?

— Spaceship could fly faster than light

— Here's what the speed of light looks like in slow motion

— Why is the speed of light the way it is?

Science fiction loves the idea of "warp speed." Faster-than-light travel makes countless sci-fi franchises possible, condensing the vast expanses of space and letting characters pop back and forth between star systems with ease. 

But while faster-than-light travel isn't guaranteed impossible, we'd need to harness some pretty exotic physics to make it work. Luckily for sci-fi enthusiasts and theoretical physicists alike, there are lots of avenues to explore.

All we have to do is figure out how to not move ourselves — since special relativity would ensure we'd be long destroyed before we reached high enough speed — but instead, move the space around us. Easy, right? 

One proposed idea involves a spaceship that could fold a space-time bubble around itself. Sounds great, both in theory and in fiction.

"If Captain Kirk were constrained to move at the speed of our fastest rockets, it would take him a hundred thousand years just to get to the next star system," said Seth Shostak, an astronomer at the Search for Extraterrestrial Intelligence (SETI) Institute in Mountain View, California, in a 2010 interview with Space.com's sister site LiveScience . "So science fiction has long postulated a way to beat the speed of light barrier so the story can move a little more quickly."

Without faster-than-light travel, any "Star Trek" (or "Star War," for that matter) would be impossible. If humanity is ever to reach the farthest — and constantly expanding — corners of our universe, it will be up to future physicists to boldly go where no one has gone before.

Additional resources

For more on the speed of light, check out this fun tool from Academo that lets you visualize how fast light can travel from any place on Earth to any other. If you’re more interested in other important numbers, get familiar with the universal constants that define standard systems of measurement around the world with the National Institute of Standards and Technology . And if you’d like more on the history of the speed of light, check out the book " Lightspeed: The Ghostly Aether and the Race to Measure the Speed of Light " (Oxford, 2019) by John C. H. Spence.

Aristotle. “On Sense and the Sensible.” The Internet Classics Archive, 350AD. http://classics.mit.edu/Aristotle/sense.2.2.html .

D’Alto, Nick. “The Pipeline That Measured the Speed of Light.” Smithsonian Magazine, January 2017. https://www.smithsonianmag.com/air-space-magazine/18_fm2017-oo-180961669/ .

Fowler, Michael. “Speed of Light.” Modern Physics. University of Virginia. Accessed January 13, 2022. https://galileo.phys.virginia.edu/classes/252/spedlite.html#Albert%20Abraham%20Michelson .

Giovannini, Daniel, Jacquiline Romero, Václav Potoček, Gergely Ferenczi, Fiona Speirits, Stephen M. Barnett, Daniele Faccio, and Miles J. Padgett. “Spatially Structured Photons That Travel in Free Space Slower than the Speed of Light.” Science, February 20, 2015. https://www.science.org/doi/abs/10.1126/science.aaa3035 .

Goldzak, Tamar, Alexei A. Mailybaev, and Nimrod Moiseyev. “Light Stops at Exceptional Points.” Physical Review Letters 120, no. 1 (January 3, 2018): 013901. https://doi.org/10.1103/PhysRevLett.120.013901 . 

Hazen, Robert. “What Makes Diamond Sparkle?” PBS NOVA, January 31, 2000. https://www.pbs.org/wgbh/nova/article/diamond-science/ . 

“How Long Is a Light-Year?” Glenn Learning Technologies Project, May 13, 2021. https://www.grc.nasa.gov/www/k-12/Numbers/Math/Mathematical_Thinking/how_long_is_a_light_year.htm . 

American Physical Society News. “July 1849: Fizeau Publishes Results of Speed of Light Experiment,” July 2010. http://www.aps.org/publications/apsnews/201007/physicshistory.cfm . 

Liu, Chien, Zachary Dutton, Cyrus H. Behroozi, and Lene Vestergaard Hau. “Observation of Coherent Optical Information Storage in an Atomic Medium Using Halted Light Pulses.” Nature 409, no. 6819 (January 2001): 490–93. https://doi.org/10.1038/35054017 . 

NIST. “Meet the Constants.” October 12, 2018. https://www.nist.gov/si-redefinition/meet-constants . 

Ouellette, Jennifer. “A Brief History of the Speed of Light.” PBS NOVA, February 27, 2015. https://www.pbs.org/wgbh/nova/article/brief-history-speed-light/ . 

Shea, James H. “Ole Ro/Mer, the Speed of Light, the Apparent Period of Io, the Doppler Effect, and the Dynamics of Earth and Jupiter.” American Journal of Physics 66, no. 7 (July 1, 1998): 561–69. https://doi.org/10.1119/1.19020 . 

Siegel, Ethan. “The Failed Experiment That Changed The World.” Forbes, April 21, 2017. https://www.forbes.com/sites/startswithabang/2017/04/21/the-failed-experiment-that-changed-the-world/ . 

Stern, David. “Rømer and the Speed of Light,” October 17, 2016. https://pwg.gsfc.nasa.gov/stargaze/Sun4Adop1.htm . 

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Vicky Stein is a science writer based in California. She has a bachelor's degree in ecology and evolutionary biology from Dartmouth College and a graduate certificate in science writing from the University of California, Santa Cruz (2018). Afterwards, she worked as a news assistant for PBS NewsHour, and now works as a freelancer covering anything from asteroids to zebras. Follow her most recent work (and most recent pictures of nudibranchs) on Twitter. 

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What is the speed of light?

Light is faster than anything else in the known universe, though its speed can change depending on what it's passing through.

The universe has a speed limit, and it's the speed of light. Nothing can travel faster than light — not even our best spacecraft — according to the laws of physics.

So, what is the speed of light? 

Light moves at an incredible 186,000 miles per second (300,000 kilometers per second), equivalent to almost 700 million mph (more than 1 billion km/h). That's fast enough to circumnavigate the globe 7.5 times in one second, while a typical passenger jet would take more than two days to go around once (and that doesn't include stops for fuel or layovers!). 

Light moves so fast that, for much of human history, we thought it traveled instantaneously. As early as the late 1600s, though, scientist Ole Roemer was able to measure the speed of light (usually referred to as c ) by using observations of Jupiter's moons, according to Britannica . 

Around the turn of the 19th century, physicist James Clerk Maxwell created his theories of electromagnetism . Light is itself made up of electric and magnetic fields, so electromagnetism could describe the behavior and motion of light — including its theoretical speed. That value was 299,788 kilometers per second, with a margin of error of plus or minus 30. In the 1970s, physicists used lasers to measure the speed of light with much greater precision, leaving an error of only 0.001. Nowadays, the speed of light is used to define units of length, so its value is fixed; humans have essentially agreed the speed of light is 299,792.458 kilometers per second, exactly.

Light doesn't always have to go so fast, though. Depending on what it's traveling through — air, water, diamonds, etc. — it can slow down. The official speed of light is measured as if it's traveling in a vacuum, a space with no air or anything to get in the way. You can most clearly see differences in the speed of light in something like a prism, where certain energies of light bend more than others, creating a rainbow.

— How many moons does Earth have ?

— What would happen if the moon were twice as close to Earth?

— If you're on the moon, does the Earth appear to go through phases?

Interestingly, the speed of light is no match for the vast distances of space, which is itself a vacuum. It takes 8 minutes for light from the sun to reach Earth, and a couple years for light from the other closest stars (like Proxima Centauri) to get to our planet. This is why astronomers use the unit light-years — the distance light can travel in one year — to measure vast distances in space.

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Because of this universal speed limit, telescopes are essentially time machines . When astronomers look at a star 500 light-years away, they're looking at light from 500 years ago. Light from around 13 billion light-years away (equivalently, 13 billion years ago) shows up as the cosmic microwave background, remnant radiation from the Big Bang in the universe's infancy. The speed of light isn't just a quirk of physics; it has enabled modern astronomy as we know it, and it shapes the way we see the world — literally.

Briley Lewis (she/her) is a freelance science writer and Ph.D. Candidate/NSF Fellow at the University of California, Los Angeles studying Astronomy & Astrophysics. Follow her on Twitter  @briles_34 or visit her website  www.briley-lewis.com .

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The Nine Planets

How Fast is the Speed of Light?

With our current understanding of motion, it seems that the speed of light is the highest of all, being 874,030 times faster than the speed of sound.

The speed of sound travels at around 343 m/s, while the speed of light travels at 299,792,458 m/s. In miles per hour/mph, the speed of light is at around 670,616,629, while in kilometers per hour, light travels at 1,079,252,848.

In terms of seconds, light travels at around 300,000 kilometers per second or 186,000 miles per second in a vacuum.

In water, the speed of light is slower, at 225,000 km / 139,808 mi per second, and 200,000 km / 124,274 mi per second in glass. It seems that nothing can be faster than the speed of light.

If you want an example of how fast the speed of light is, think about this, if we were to launch an imaginary spacecraft from Earth that would travel at around 153,454 mi / 246,960 km per hour constantly, it would reach the Sun in 606 hours, or 25 days. 

However, if our spacecraft would be traveling at the speed of light, we would reach the Sun in only 8.3 minutes. If you traveled around the Earth with the speed of light, you would make a complete tour of our planet 7.5 times in just one second.

In theory, it seems that nothing is faster than the speed of light, or is there? Let’s find out.

Is There Anything Faster Than the Speed of Light?

It appears that nothing is faster than the speed of light, but the Universe , as always, eludes our perception once again. Scientists have demonstrated that the Universe is expanding, and this expansion is even faster than the speed of light.

Since space is theoretically “nothing,” it isn’t susceptible to the laws of physics. If you were to hold a torch and run with it, the speed of its light would still travel at the same rate.

Some galaxies are moving away from our Milky Way faster than the speed of light, and this is happening because space itself is moving along with them.

If there were something more efficient than traveling with the speed of light, it would be traveling through wormholes. Wormholes are hypothetical, but their mechanism is quite intriguing, and in a way, if it were possible, they are supposedly faster than the speed of light.

This is because a wormhole connects two distant points, and, in theory, if you were to travel from point a to b, regardless of its distance, you would reach your destination extremely fast.

How Fast is the Speed of Dark?

Many consider that the speed of darkness is simply a poetic metaphor and wouldn’t have any legitimate scientific basis, since dark is simply the absence of light.

However, this may seem a bit more complicated. If we were to put a dark spot in a beam of light, darkness would theoretically move at the same speed as light.

The same holds true if we would illuminate a dark corner. It is uncertain if darkness itself has a speed, but when it comes to dark matter, things start to unfold.

Dark matter is hypothetical energy, which makes up more than 80% of our Universe. In some studies, scientists estimated that this mysterious element might travel at around 54 m/s, to equate for its existence, but this is quite slow when compared to the speed of light.

Things get complicated if we look at black holes as part of the definition of darkness. Black holes are devoid of light, and if anything gets near their event horizon, not even light can escape from them.

Some black holes are fast-spinner as well, with some of them being recorded with having a spinning speed of around 84% of the speed of light. Darkness or the speed of dark is quite a fascinating subject, but it remains elusive to our current understanding.

What is the Fastest Thing in the Universe?

The fastest thing in the Universe, based on our current knowledge, is light. If you want to play dirty, you could say that the Universe/space is the fastest thing in existence, since it expands with a speed even faster than the speed of light.

If, in the future, we will understand how black holes can capture even light, maybe some of their mechanisms are the fastest thing in the Universe.

What Would Happen if You Would Travel Faster Than the Speed of Light?

The theory of special relativity states that nothing should travel faster than the speed of light, and if something does so, it will move backward in time.

Traveling faster than the speed of light might simply mean time travel. However, is this were true, in some ways, you might as well achieve immortality, as no cause could affect you, not even time, especially if, hypothetically speaking, you wouldn’t even be subjected to the impacts of the objects you would travel through.

Our current understanding of light speed is minimal, and even more so when it comes to surpassing it. We, as a species, with our current technology, have only just reached small percentages of the speed of light. We aren’t even halfway there.

What is the 2 nd Fastest Thing in the Universe?

Blobs of hot gas embedded in streams of material ejected from blazars, which are highly active galaxies , travel at around 99.9% of the speed of light.

Thus, the physical processes that occur at the cores of blazars are so energetic that they can propel matter quite close to light speed, and as such, they are probably the second fastest thing in the Universe. 

Did you know?

The fastest speed reached by a land vehicle is the ThrustSSC supersonic car. This vehicle reached 1,227 km / 772 mi/h, and it maintains its title as the most rapid land vehicle since 1997.

The fastest plane/aircraft in the world is the Lockheed SR-71 Black Bird. It achieved this title in 1976, and it reached a speed of 3,529.6 km/ 2,192 mi per hour.

The Parker Solar Probe is currently the fastest spacecraft ever designed by man. It reached 153,454 miles / 246,960 kilometers per hour.

Image Sources:

• https://images.immediate.co.uk/production/volatile/sites/4/2018/08/GettyImages-524396835-bca79f7.jpg?quality=90&resize=960%2C408
• https://cdn.britannica.com/s:800×450,c:crop/83/179683-138-D3C80B7C/Scientists-speed-of-light.jpg
• https://cdn.hswstatic.com/gif/speed-of-darkness-orig.jpg
• https://4.bp.blogspot.com/-7qK2eGoouKI/TprUhQT6hcI/AAAAAAAAEww/BHe3uF_S-rU/s1600/Time-travel-through-a-wormhole-thumb-550xauto-38205.jpg
• https://i.insider.com/5b47524e744a9820008b4838?width=1100&format=jpeg&auto=webp

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What Is the Speed of Light?

The speed of light is the rate at which light travels. The speed of light in a vacuum is a constant value that is denoted by the letter c and is defined as exactly 299,792,458 meters per second. Visible light , other electromagnetic radiation, gravity waves, and other massless particles travel at c. Matter , which has mass, can approach the speed of light, but never reach it.

Value for the Speed of Light in Different Units

Here are values for the speed of light in various units:

• 299,792,458 meters per second ( exact number )
• 299,792 kilometers per second (rounded)
• 3×10 8 m/s (rounded)
• 186,000 miles per second (rounded)
• 671,000,000 miles per hour (rounded)
• 1,080,000,000 kilometers per hour (rounded)

Is the Speed of Light Really Constant?

The speed of light in a vacuum is a constant. However, scientists are exploring whether the speed of light has changed over time.

Also, the rate at which light travels changes as it passes through a medium. The index of refraction describes this change. For example, the index of refraction of water is 1.333, which means light travels 1.333 times slower in water than in a vacuum. The index of refraction of a diamond is 2.417. A diamond slows the speed of light by more than half its speed in a vacuum.

How to Measure the Speed of Light

One way of measuring the speed of light uses great distances, such as distant points on the Earth or known distances between the Earth and astronomical objects. For example, you can measure the speed of light by measuring the time it takes for light to travel from a light source to a distant mirror and back again. The other way of measuring the speed of light is solving for c in equations. Now that the speed of light is defined, it is fixed rather than measured. Measuring the speed of light today indirectly measures the length of the meter, rather than c .

In 1676, Danish astronomer Ole Rømer discovered light travels at a speed by studying the movement of Jupiter’s moon Io. Prior to this, it seemed light propagated instantaneously. For example, you see a lightning strike immediately, but don’t hear thunder until after the event . So, Rømer’s finding showed light takes time to travel, but scientists did not know the speed of light or whether it was constant. In 1865, James Clerk Maxwell proposed that light was an electromagnetic wave that travelled at a speed c . Albert Einstein suggested c was a constant and that it did not change according to the frame of reference of the observer or any motion of a light source. In other words, Einstein suggested the speed of light is invariant . Since then, numerous experiments have verified the invariance of c .

Is It Possible to Go Faster Than Light?

The upper speed limit for massless particles is c . Objects that have mass cannot travel at the speed of light or exceed it. Among other reasons, traveling at c gives an object a length of zero and infinite mass. Accelerating a mass to the speed of light requires infinite energy. Furthermore, energy, signals, and individual photos cannot travel faster than c . At first glance, quantum entanglement appears to transmit information faster than c . When two particles are entangled, changing the state of one particle instantaneously determines the state of the other particle, regardless of the distance between them. But, information cannot be transmitted instantaneously (faster than c ) because it isn’t possible to control the initial quantum state of the particle when it is observed.

However, faster-than-light speeds appear in physics. For example, the phase velocity of x-rays through glass often exceeds c. However, the information isn’t conveyed by the waves faster than the speed of light. Distant galaxies appear to move away from Earth faster than the speed of light (outside a distance called the Hubble sphere), but the motion isn’t due to the galaxies traveling through space. Instead, space itself it expanding. So again, no actual movement faster than c occurs.

While it isn’t possible to go faster than the speed of light, it doesn’t necessarily mean warp drive or other faster-than-light travel is impossible. The key to going faster than the speed of light is to change space-time. Ways this might happen include tunneling using wormholes or stretching space-time into a “warp bubble” around a spacecraft. But, so far these theories don’t have practical applications.

• Brillouin, L. (1960). Wave Propagation and Group Velocity. Academic Press.
• Ellis, G.F.R.; Uzan, J.-P. (2005). “‘c’ is the speed of light, isn’t it?”. American Journal of Physics . 73 (3): 240–27. doi: 10.1119/1.1819929
• Helmcke, J.; Riehle, F. (2001). “Physics behind the definition of the meter”. In Quinn, T.J.; Leschiutta, S.; Tavella, P. (eds.). Recent advances in metrology and fundamental constants . IOS Press. p. 453. ISBN 978-1-58603-167-1.
• Newcomb, S. (1886). “The Velocity of Light”. Nature . 34 (863): 29–32. doi: 10.1038/034029c0
• Uzan, J.-P. (2003). “The fundamental constants and their variation: observational status and theoretical motivations”. Reviews of Modern Physics . 75 (2): 403. doi: 10.1103/RevModPhys.75.403

Related Posts

What is a light-year?

Light-year is the distance light travels in one year. Light zips through interstellar space at 186,000 miles (300,000 kilometers) per second and 5.88 trillion miles (9.46 trillion kilometers) per year.

We use light-time to measure the vast distances of space.

It’s the distance that light travels in a specific period of time. Also: LIGHT IS FAST, nothing travels faster than light.

How far can light travel in one minute? 11,160,000 miles. It takes 43.2 minutes for sunlight to reach Jupiter, about 484 million miles away. Light is fast, but the distances are vast . In an hour, light can travel 671 million miles.

Earth is about eight light minutes from the Sun. A trip at light-speed to the very edge of our solar system – the farthest reaches of the Oort Cloud, a collection of dormant comets way, way out there – would take about 1.87 years. Keep going to Proxima Centauri, our nearest neighboring star, and plan on arriving in 4.25 years at light speed.

When we talk about the enormity of the cosmos, it’s easy to toss out big numbers – but far more difficult to wrap our minds around just how large, how far, and how numerous celestial bodies really are.

To get a better sense, for instance, of the true distances to exoplanets – planets around other stars – we might start with the theater in which we find them, the Milky Way galaxy.

Our galaxy is a gravitationally bound collection of stars, swirling in a spiral through space. Based on the deepest images obtained so far, it’s one of about 2 trillion galaxies in the observable universe. Groups of them are bound into clusters of galaxies, and these into superclusters; the superclusters are arranged in immense sheets stretching across the universe, interspersed with dark voids and lending the whole a kind of spiderweb structure. Our galaxy probably contains 100 to 400 billion stars, and is about 100,000 light-years across. That sounds huge, and it is, at least until we start comparing it to other galaxies. Our neighboring Andromeda galaxy, for example, is some 220,000 light-years wide. Another galaxy, IC 1101, spans as much as 4 million light-years.

Based on observations by NASA’s Kepler Space Telescope, we can confidently predict that every star you see in the sky probably hosts at least one planet. Realistically, we’re most likely talking about multi-planet systems rather than just single planets. In our galaxy of hundreds of billions of stars, this pushes the number of planets potentially into the trillions. Confirmed exoplanet detections (made by Kepler and other telescopes, both in space and on the ground) now come to more than 4,000 – and that’s from looking at only tiny slices of our galaxy. Many of these are small, rocky worlds that might be at the right temperature for liquid water to pool on their surfaces.

The nearest-known exoplanet is a small, probably rocky planet orbiting Proxima Centauri – the next star over from Earth. A little more than four light-years away, or 24 trillion miles. If an airline offered a flight there by jet, it would take 5 million years. Not much is known about this world; its close orbit and the periodic flaring of its star lower its chances of being habitable.

The TRAPPIST-1 system is seven planets, all roughly in Earth’s size range, orbiting a red dwarf star about 40 light-years away. They are very likely rocky, with four in the “habitable zone” – the orbital distance allowing potential liquid water on the surface. And computer modeling shows some have a good chance of being watery – or icy – worlds. In the next few years, we might learn whether they have atmospheres or oceans, or even signs of habitability.

One of the most distant exoplanets known to us in the Milky Way is Kepler-443 b. Traveling at light speed, it would take 3,000 years to get there. Or 28 billion years, going 60 mph.

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Black Holes

The speed of light is torturously slow, and these 3 simple animations by a scientist at NASA prove it

• The speed of light in a vacuum is about 186,282 miles per second (299,792 kilometers per second).
• A scientist at NASA animated how long it takes light to travel around Earth, as well as between the planet, its moon, and Mars.
• The physics animations show just how fast (and slow) the speed limit of the universe can be.

A series of new animations by a NASA scientist show just how zippy — and also how torturously slow — the speed of light can be.

Light speed is the fastest that any material object can travel through space. That is, of course, barring the existence of theoretical shortcuts in the fabric of space called wormholes (and the ability to go through them without being destroyed).

In a perfectly empty vacuum, a particle of light, which is called a photon, can travel 186,282 miles per second (299,792 kilometers per second), or about 670.6 million mph (1.079 billion kilometers per hour).

This is incredibly fast. However, light speed can be frustratingly slow if you're trying to communicate with or reach other planets, especially any worlds beyond our solar system.

Read more : Astronomers found a 'cold super-Earth' less than 6 light-years away — and it may be the first rocky planet we'll photograph beyond the solar system

To depict the speed limit of the cosmos in a way anyone could understand, James O'Donoghue , a planetary scientist at NASA's Goddard Space Flight Center, took it upon himself to animate it.

"My animations were made to show as instantly as possible the whole context of what I'm trying to convey," O'Donoghue told Business Insider via Twitter . "When I revised for my exams, I used to draw complex concepts out by hand just to truly understand, so that's what I'm doing here."

O'Donoghue said he only recently learned how to create these animations — his first were for a NASA news release about Saturn's vanishing rings . After that, he moved on to animating other difficult-to-grasp space concepts, including a video illustrating the rotation speeds and sizes of the planets. He said that one "garnered millions of views" when he posted it on Twitter .

O'Donoghue's latest effort looks at three different light-speed scenarios to convey how fast (and how painfully slow) photons can be.

How fast light travels relative to Earth

One of O'Donoghue's first animations shows how fast light moves in relation to Earth.

Earth is 24,901 miles around at its center. If our world had no atmosphere (air refracts and slows down light a little bit), a photon skimming along its surface could lap the equator nearly 7.5 times every second.

In this depiction , the speed of light seems pretty fast — though the movie also shows how finite it is.

How fast light travels between Earth and the moon

A second animation by O'Donoghue takes a big step back from Earth to include the moon.

Related stories

On average, there is about 238,855 miles (384,400 kilometers) of distance between our planet and its large natural satellite.

This means all moonlight we see is 1.255 seconds old, and a round-trip between the Earth and moon at light speed takes about 2.51 seconds.

This timing is growing every day, however, as the moon is drifting farther from Earth at a rate of about 1.5 inches (3.8 centimeters) per year. (The moon is constantly sapping Earth's rotational energy via ocean tides , boosting its orbit to a greater and greater distance.)

How fast light travels between Earth and Mars

O'Donoghue's third speed-of-light animation illustrates the challenge that many planetary scientists deal with on a daily basis.

When NASA tries to talk to or download data from a spacecraft, such as the InSight probe on Mars , it can do so only at the speed of light. This is much too slow to operate a spacecraft in "live mode" as you would a remote-controlled car. So, commands must be carefully thought out, prepackaged, and aimed at the precise location in space at the precise time so that they don't miss their target.

Read more : NASA can hear the 'haunting' sound of dust devils tearing across Mars with its new $830 million lander

The fastest a conversation could ever happen between Earth and Mars is when the planets are at their nearest point to one another, an event called closest approach that happens once roughly every two years. On average, that best-case-scenario distance is about 33.9 million miles (54.6 million kilometers).

As that 60-second clip of O'Donoghue's full movie on YouTube shows, light takes 3 minutes 2 seconds to travel between Earth and Mars at closest approach. That's six minutes and four seconds for a light-speed round-trip.

But on average, Mars is about 158 million miles from Earth — so the average round-trip communication takes about 28 minutes and 12 seconds.

The speed of light gets more depressing the farther you go

The hurdle of light's finite speed gets even more challenging for spacecraft such as New Horizons, which is now more than 4 billion miles from Earth , and the Voyager 1 and 2 spacecraft, each of which have reached the space between stars .

The situation gets downright depressing when you start looking outside the solar system. The closest-known exoplanet , called Proxima b, is about 4.2 light-years away from us (a distance of about 24.7 trillion miles or 39.7 trillion kilometers).

However, the fastest any spacecraft has ever gone is NASA's Parker Solar Probe at about 213,200 mph ; at that speed, it'd take 13,211 years to reach Proxima b.

A Russian-American billionaire's Breakthrough Starshot project envisions a way to address this speed problem. The multidecade plan is to build and fly tiny "nanocraft" past such exoplanets via ultrapowerful laser blasts , ideally at a planned cruise velocity of 20% of the speed of light. Yet the entire concept is still theoretical, may end up not working, and would operate at a fraction of light-speed.

Space is impossibly vast. Although the universe is about 13.77 billion years old, its edge is about 45.34 billion light-years away in any direction and is increasing due to expansion .

That's far too big to illustrate in a simple animation. One illustration comes close, though: this image created by musician Pablo Carlos Budassi , which combines logarithmic maps of the universe from Princeton and images from NASA to capture it all in one picture.

This story has been updated.

Watch: What humans will look like on Mars

• Main content

What Is a Light-Year?

An image of distant galaxies captured by the NASA/ESA Hubble Space Telescope. Credit: ESA/Hubble & NASA, RELICS; Acknowledgment: D. Coe et al.

For most space objects, we use light-years to describe their distance. A light-year is the distance light travels in one Earth year. One light-year is about 6 trillion miles (9 trillion km). That is a 6 with 12 zeros behind it!

Looking Back in Time

When we use powerful telescopes to look at distant objects in space, we are actually looking back in time. How can this be?

Light travels at a speed of 186,000 miles (or 300,000 km) per second. This seems really fast, but objects in space are so far away that it takes a lot of time for their light to reach us. The farther an object is, the farther in the past we see it.

Our Sun is the closest star to us. It is about 93 million miles away. So, the Sun's light takes about 8.3 minutes to reach us. This means that we always see the Sun as it was about 8.3 minutes ago.

The next closest star to us is about 4.3 light-years away. So, when we see this star today, we’re actually seeing it as it was 4.3 years ago. All of the other stars we can see with our eyes are farther, some even thousands of light-years away.

Stars are found in large groups called galaxies . A galaxy can have millions or billions of stars. The nearest large galaxy to us, Andromeda, is 2.5 million light-years away. So, we see Andromeda as it was 2.5 million years in the past. The universe is filled with billions of galaxies, all farther away than this. Some of these galaxies are much farther away.

An image of the Andromeda galaxy, as seen by NASA's GALEX observatory. Credit: NASA/JPL-Caltech

In 2016, NASA's Hubble Space Telescope looked at the farthest galaxy ever seen, called GN-z11. It is 13.4 billion light-years away, so today we can see it as it was 13.4 billion years ago. That is only 400 million years after the big bang . It is one of the first galaxies ever formed in the universe.

Learning about the very first galaxies that formed after the big bang, like this one, helps us understand what the early universe was like.

This picture shows hundreds of very old and distant galaxies. The oldest one found so far in GN-z11 (shown in the close up image). The image is a bit blurry because this galaxy is so far away. Credit: NASA, ESA, P. Oesch (Yale University), G. Brammer (STScI), P. van Dokkum (Yale University), and G. Illingworth (University of California, Santa Cruz)

More to explore

What Is a Galaxy?

How Far Away Is the Moon?

What Is a Nebula?

If you liked this, you may like:

Universe Today

Space and astronomy news

How Far Does Light Travel in a Year?

The Universe is an extremely big place. As astronomers looked farther into space over the centuries, and deeper into the past, they came to understand just how small and insignificant our planet and our species seem by comparison. At the same time, ongoing investigations into electromagnetism and distant stars led scientists to deduce what the the speed of light is – and that it is the fastest speed obtainable.

As such, astronomers have taken to using the the distance light travels within a single year (aka. a light year) to measure distances on the interstellar and intergalactic scale. But how far does light travel in a year? Basically, it moves at a speed of 299,792,458 meters per second ( 1080 million km/hour; 671 million mph), which works out to about 9,460.5 trillion km (5,878.5 trillion miles) per year.

The Speed of Light:

Calculating the speed of light has been a preoccupation for scientists for many centuries. And prior to the 17th century, there was disagreement over whether the speed of light was finite, or if it moved from one spot to the next instantaneously. In 1676, Danish astronomer Ole Romer settled the argument when his observations of the apparent motion of Jupiter’s moon Io revealed that the speed of light was finite.

From his observations, famed Dutch astronomer Christiaan Huygens calculated the speed of light at 220,000 km/s (136,701 mi/s). Over the course of the nest two centuries, the speed of light was refined further and further, producing estimates that ranged from about 299,000 to 315,000 km/s (185,790 to 195,732 mi/s).

This was followed by James Clerk Maxwell, who proposed in 1865 that light was an electromagnetic wave. In his theory of electromagnetism, the speed of light was represented as c. And then in 1905, Albert Einstein proposed his theory of Special Relativity , which postulated that the speed of light ( c ) was constant, regardless of the inertial reference frame of the observer or the motion of the light source.

By 1975, after centuries of refined measurements, the speed of light in a vacuum was calculated at 299,792,458 meters per second. Ongoing research also revealed that light travels at different wavelengths and is made up of subatomic particles known as photons, which have no mass and behave as both particles and waves.

Light-Year:

As already noted, the speed of light (expressed in meters per second) means that light travels a distance of 9,460,528,000,000 km (or 5,878,499,817,000 miles) in a single year. This distance is known as a “light year”, and is used to measure objects in the Universe that are at a considerable distances from us.

For example, the nearest star to Earth (Proxima Centauri) is roughly 4.22 light-years distant. The center of the Milky Way Galaxy is 26,000 light-years away, while the nearest large galaxy (Andromeda) is 2.5 million light-years away. To date, the candidate for the farthest galaxy from Earth is MACS0647-JD , which is located approximately 13.3 billion light years away.

And the Cosmic Microwave Background , the relic radiation which is believed to be leftover from the Big Bang, is located some 13.8 billion light years away. The discovery of this radiation not only bolstered the Big Bang Theor y, but also gave astronomers an accurate assessment of the age of the Universe. This brings up another important point about measuring cosmic distances in light years, which is the fact that space and time are intertwined.

You see, when we see the light coming from a distant object, we’re actually looking back in time. When we see the light from a star located 400 light-years away, we’re actually seeing light that was emitted from the star 400 years ago. Hence, we’re seeing the star as it looked 400 years ago, not as it appears today. As a result, looking at objects billions of light-years from Earth is to see billions of light-years back in time.

Yes, light travels at an extremely fast speed. But given the sheer size and scale of the Universe, it can still take billions of years from certain points in the Universe to reach us here on Earth. Hence why knowing how long it takes for light to travel a single year is so useful to scientists. Not only does it allow us to comprehend the scale of the Universe, it also allows us to chart the process of cosmic evolution.

We have written many articles about the speed of light here at Universe Today. Here’s How Far is a Light Year? , What is the Speed of Light ?, How Much Stuff is in a Light Year? , How Does Light Travel? , and How Far Can You See in the Universe?

Want more info on light-years? Here’s an article about light-years for HowStuffWorks , and here’s an answer from PhysLink .

We’ve also recorded an episode of Astronomy Cast on this topic. Listen here, Episode 10: Measuring Distance in the Universe .

• NASA – How Fast is the Speed of Light?
• NASA: Starchild – What is a Light-Year and How is it Measured?
• Wikipedia – Speed of Light
• UCR – How is the Speed of Light Measured?

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3 Replies to “How Far Does Light Travel in a Year?”

Time and measurement are both man made entities. Time is basically a year, broken down into seconds. Measurement is derived from some guys thumb. Consider if humans were 100 times bigger, and measurement evolved the same way, the speed of light would be 100 times slower. Conversely if humans were 100 times smaller the SOL would be 100 times faster. Now consider if we grew up on Jupiter, that has a 10 hour day and a year is 11.8 Earth years. Thats 10,500 jovian days to a jovian year. Seconds would evolve differently on that planet. So how do we know we are correct with the SOL when both sides of the equation are made up bits of fantasy. Cheers Steven.

How we measure time is based on our inertial reference frame. That comes from being at the bottom of a 1 g gravity well, and to the time it takes the planet to rotate once on its axis and once around the Sun. The size of our thumbs or our bodies is completely irrelevant and being larger would change nothing. The same goes for if we were traveling through space, our perception of time would be based on our speed – i.e. our inertial reference frame.

And time itself is not man-made, its a fundamental part of the Universe and the laws which govern it. This is not fantasy, its physics.

You wrote : “fellow Danish astronomer Christiaan Huygens “, that is not right. Christiaan Huygens was a Dutch (Netherland) scientist.

Comments are closed.

Light Year Calculator

Table of contents

With this light year calculator, we aim to help you calculate the distance that light can travel in a certain amount of time . You can also check out our speed of light calculator to understand more about this topic.

We have written this article to help you understand what a light year is and how to calculate a light year using the light year formula . We will also demonstrate some examples to help you understand the light year calculation.

What is light year?

A light year is a unit of measurement used in astronomy to describe the distance that light travels in one year . Since light travels at a speed of approximately 186,282 miles per second (299,792,458 meters per second), a light year is a significant distance — about 5.88 trillion miles (9.46 trillion km) . Please check out our distance calculator to understand more about this topic.

The concept of a light year is important for understanding the distances involved in space exploration. Since the universe is so vast, it's often difficult to conceptualize the distances involved in astronomical measurements. However, by using a light year as a unit of measurement, scientists and astronomers can more easily compare distances between objects in space.

How to calculate light years?

As the light year is a unit of measure for the distance light can travel in a year , this concept can help us to calculate the distance that light can travel in a certain time period. Hence, let's have a look at the following example:

• Source: Light
• Speed of light: 299,792,458 m/s
• Time traveled: 2 years

You can perform the calculation in three steps:

Determine the speed of light.

The speed of light is the fastest speed in the universe, and it is always a constant in a vacuum. Hence, the speed of light is 299,792,458 m/s , which is 9.46×10¹² km/year .

Compute the time that the light has traveled.

The subsequent stage involves determining the duration of time taken by the light to travel. Since we are interested in light years, we will be measuring the time in years.

To facilitate this calculation, you may use our time lapse calculator . In this specific scenario, the light has traveled for a duration of 2 years.

Calculate the distance that the light has traveled.

The final step is to calculate the total distance that the light has traveled within the time . You can calculate this answer using the speed of light formula:

distance = speed of light × time

Thus, the distance that the light can travel in 100 seconds is 9.46×10¹² km/year × 2 years = 1.892×10¹³ km

How do I calculate the distance that light travels?

You can calculate the distance light travels in three steps:

Determine the light speed .

Determine the time the light has traveled.

Apply the light year formula :

distance = light speed × time

How far light can travel in 1 second?

The light can travel 186,282 miles, or 299,792,458 meters, in 1 second . That means light can go around the Earth just over 7 times in 1 second.

Why is the concept of a light year important in astronomy?

The concept of a light year is important in astronomy because it helps scientists and astronomers more easily compare distances between objects in space and understand the vastness of the universe .

Can light years be used to measure time?

No , despite the name, you cannot use light years to measure time. They only measure distance .

Speed of light

Chapter 15: Galaxies

Chapter 1 how science works.

• The Scientific Method
• Measurements
• Units and the Metric System
• Measurement Errors
• Mass, Length, and Time
• Observations and Uncertainty
• Precision and Significant Figures
• Errors and Statistics
• Scientific Notation
• Ways of Representing Data
• Mathematics
• Testing a Hypothesis
• Case Study of Life on Mars
• Systems of Knowledge
• The Culture of Science
• Computer Simulations
• Modern Scientific Research
• The Scope of Astronomy
• Astronomy as a Science
• A Scale Model of Space
• A Scale Model of Time

Chapter 2 Early Astronomy

• The Night Sky
• Motions in the Sky
• Constellations and Seasons
• Cause of the Seasons
• The Magnitude System
• Angular Size and Linear Size
• Phases of the Moon
• Dividing Time
• Solar and Lunar Calendars
• History of Astronomy
• Ancient Observatories
• Counting and Measurement
• Greek Astronomy
• Aristotle and Geocentric Cosmology
• Aristarchus and Heliocentric Cosmology
• The Dark Ages
• Arab Astronomy
• Indian Astronomy
• Chinese Astronomy
• Mayan Astronomy

Chapter 3 The Copernican Revolution

• Ptolemy and the Geocentric Model
• The Renaissance
• Copernicus and the Heliocentric Model
• Tycho Brahe
• Johannes Kepler
• Elliptical Orbits
• Kepler's Laws
• Galileo Galilei
• The Trial of Galileo
• Isaac Newton
• Newton's Law of Gravity
• The Plurality of Worlds
• The Birth of Modern Science
• Layout of the Solar System
• Scale of the Solar System
• The Idea of Space Exploration
• History of Space Exploration
• Moon Landings
• International Space Station
• Manned versus Robotic Missions
• Commercial Space Flight
• Future of Space Exploration
• Living in Space
• Moon, Mars, and Beyond
• Societies in Space

Chapter 4 Matter and Energy in the Universe

• Matter and Energy
• Rutherford and Atomic Structure
• Early Greek Physics
• Dalton and Atoms
• The Periodic Table
• Structure of the Atom
• Heat and Temperature
• Potential and Kinetic Energy
• Conservation of Energy
• Velocity of Gas Particles
• States of Matter
• Thermodynamics
• Laws of Thermodynamics
• Heat Transfer
• Thermal Radiation
• Radiation from Planets and Stars
• Internal Heat in Planets and Stars
• Periodic Processes
• Random Processes

Chapter 5 The Earth-Moon System

• Earth and Moon
• Early Estimates of Earth's Age
• How the Earth Cooled
• Ages Using Radioactivity
• Radioactive Half-Life
• Ages of the Earth and Moon
• Geological Activity
• Internal Structure of the Earth and Moon
• Basic Rock Types
• Layers of the Earth and Moon
• Origin of Water on Earth
• The Evolving Earth
• Plate Tectonics
• Geological Processes
• Impact Craters
• The Geological Timescale
• Mass Extinctions
• Evolution and the Cosmic Environment
• Earth's Atmosphere and Oceans
• Weather Circulation
• Environmental Change on Earth
• The Earth-Moon System
• Geological History of the Moon
• Tidal Forces
• Effects of Tidal Forces
• Historical Studies of the Moon
• Lunar Surface
• Ice on the Moon
• Origin of the Moon
• Humans on the Moon

Chapter 6 The Terrestrial Planets

• Studying Other Planets
• The Planets
• The Terrestrial Planets
• Mercury's Orbit
• Mercury's Surface
• Volcanism on Venus
• Venus and the Greenhouse Effect
• Tectonics on Venus
• Exploring Venus
• Mars in Myth and Legend
• Early Studies of Mars
• Mars Close-Up
• Modern Views of Mars
• Missions to Mars
• Geology of Mars
• Water on Mars
• Polar Caps of Mars
• Climate Change on Mars
• Terraforming Mars
• Life on Mars
• The Moons of Mars
• Martian Meteorites
• Comparative Planetology
• Incidence of Craters
• Counting Craters
• Counting Statistics
• Internal Heat and Geological Activity
• Magnetic Fields of the Terrestrial Planets
• Mountains and Rifts
• Radar Studies of Planetary Surfaces
• Laser Ranging and Altimetry
• Gravity and Atmospheres
• Normal Atmospheric Composition
• The Significance of Oxygen

Chapter 7 The Giant Planets and Their Moons

• The Gas Giant Planets
• Atmospheres of the Gas Giant Planets
• Clouds and Weather on Gas Giant Planets
• Internal Structure of the Gas Giant Planets
• Thermal Radiation from Gas Giant Planets
• Life on Gas Giant Planets?
• Why Giant Planets are Giant
• Ring Systems of the Giant Planets
• Structure Within Ring Systems
• The Origin of Ring Particles
• The Roche Limit
• Resonance and Harmonics
• Tidal Forces in the Solar System
• Moons of Gas Giant Planets
• Geology of Large Moons
• The Voyager Missions
• Jupiter's Galilean Moons
• Jupiter's Ganymede
• Jupiter's Europa
• Jupiter's Callisto
• Jupiter's Io
• Volcanoes on Io
• Cassini Mission to Saturn
• Saturn's Titan
• Saturn's Enceladus
• Discovery of Uranus and Neptune
• Uranus' Miranda
• Neptune's Triton
• The Discovery of Pluto
• Pluto as a Dwarf Planet
• Dwarf Planets

Chapter 8 Interplanetary Bodies

• Interplanetary Bodies
• Early Observations of Comets
• Structure of the Comet Nucleus
• Comet Chemistry
• Oort Cloud and Kuiper Belt
• Kuiper Belt
• Comet Orbits
• Life Story of Comets
• The Largest Kuiper Belt Objects
• Meteors and Meteor Showers
• Gravitational Perturbations
• Surveys for Earth Crossing Asteroids
• Asteroid Shapes
• Composition of Asteroids
• Introduction to Meteorites
• Origin of Meteorites
• Types of Meteorites
• The Tunguska Event
• The Threat from Space
• Probability and Impacts
• Impact on Jupiter
• Interplanetary Opportunity

Chapter 9 Planet Formation and Exoplanets

• Formation of the Solar System
• Early History of the Solar System
• Conservation of Angular Momentum
• Angular Momentum in a Collapsing Cloud
• Helmholtz Contraction
• Safronov and Planet Formation
• Collapse of the Solar Nebula
• Why the Solar System Collapsed
• From Planetesimals to Planets
• Accretion and Solar System Bodies
• Differentiation
• Planetary Magnetic Fields
• The Origin of Satellites
• Solar System Debris and Formation
• Gradual Evolution and a Few Catastrophies
• Chaos and Determinism
• Extrasolar Planets
• Discoveries of Exoplanets
• Doppler Detection of Exoplanets
• Transit Detection of Exoplanets
• The Kepler Mission
• Direct Detection of Exoplanets
• Properties of Exoplanets
• Implications of Exoplanet Surveys
• Future Detection of Exoplanets

Chapter 10 Detecting Radiation from Space

• Observing the Universe
• Radiation and the Universe
• The Nature of Light
• The Electromagnetic Spectrum
• Properties of Waves
• Waves and Particles
• How Radiation Travels
• Properties of Electromagnetic Radiation
• The Doppler Effect
• Invisible Radiation
• Thermal Spectra
• The Quantum Theory
• The Uncertainty Principle
• Spectral Lines
• Emission Lines and Bands
• Absorption and Emission Spectra
• Kirchoff's Laws
• Astronomical Detection of Radiation
• The Telescope
• Optical Telescopes
• Optical Detectors
• Adaptive Optics
• Image Processing
• Digital Information
• Radio Telescopes
• Telescopes in Space
• Hubble Space Telescope
• Interferometry
• Collecting Area and Resolution
• Frontier Observatories

Chapter 11 Our Sun: The Nearest Star

• The Nearest Star
• Properties of the Sun
• Kelvin and the Sun's Age
• The Sun's Composition
• Energy From Atomic Nuclei
• Mass-Energy Conversion
• Examples of Mass-Energy Conversion
• Energy From Nuclear Fission
• Energy From Nuclear Fusion
• Nuclear Reactions in the Sun
• The Sun's Interior
• Energy Flow in the Sun
• Collisions and Opacity
• Solar Neutrinos
• Solar Oscillations
• The Sun's Atmosphere
• Solar Chromosphere and Corona
• The Solar Cycle
• The Solar Wind
• Effects of the Sun on the Earth
• Cosmic Energy Sources

Chapter 12 Properties of Stars

• Star Properties
• The Distance to Stars
• Apparent Brightness
• Absolute Brightness
• Measuring Star Distances
• Stellar Parallax
• Spectra of Stars
• Spectral Classification
• Temperature and Spectral Class
• Stellar Composition
• Stellar Motion
• Stellar Luminosity
• The Size of Stars
• Stefan-Boltzmann Law
• Stellar Mass
• Hydrostatic Equilibrium
• Stellar Classification
• The Hertzsprung-Russell Diagram
• Volume and Brightness Selected Samples
• Stars of Different Sizes
• Understanding the Main Sequence
• Stellar Structure
• Stellar Evolution

Chapter 13 Star Birth and Death

• Star Birth and Death
• Understanding Star Birth and Death
• Cosmic Abundance of Elements
• Star Formation
• Molecular Clouds
• Young Stars
• T Tauri Stars
• Mass Limits for Stars
• Brown Dwarfs
• Young Star Clusters
• Cauldron of the Elements
• Main Sequence Stars
• Nuclear Reactions in Main Sequence Stars
• Main Sequence Lifetimes
• Evolved Stars
• Cycles of Star Life and Death
• The Creation of Heavy Elements
• Horizontal Branch and Asymptotic Giant Branch Stars
• Variable Stars
• Magnetic Stars
• Stellar Mass Loss
• White Dwarfs
• Seeing the Death of a Star
• Supernova 1987A
• Neutron Stars and Pulsars
• Special Theory of Relativity
• General Theory of Relativity
• Black Holes
• Properties of Black Holes

Chapter 14 The Milky Way

• The Distribution of Stars in Space
• Stellar Companions
• Binary Star Systems
• Binary and Multiple Stars
• Mass Transfer in Binaries
• Binaries and Stellar Mass
• Nova and Supernova
• Exotic Binary Systems
• Gamma Ray Bursts
• How Multiple Stars Form
• Environments of Stars
• The Interstellar Medium
• Effects of Interstellar Material on Starlight
• Structure of the Interstellar Medium
• Dust Extinction and Reddening
• Groups of Stars
• Open Star Clusters
• Globular Star Clusters
• Distances to Groups of Stars
• Ages of Groups of Stars
• Layout of the Milky Way
• William Herschel
• Isotropy and Anisotropy
• Mapping the Milky Way

Chapter 15 Galaxies

• The Milky Way Galaxy
• Mapping the Galaxy Disk
• Spiral Structure in Galaxies
• Mass of the Milky Way
• Dark Matter in the Milky Way
• Galaxy Mass
• The Galactic Center
• Black Hole in the Galactic Center
• Stellar Populations
• Formation of the Milky Way
• The Shapley-Curtis Debate
• Edwin Hubble
• Distances to Galaxies
• Classifying Galaxies
• Spiral Galaxies
• Elliptical Galaxies
• Lenticular Galaxies
• Dwarf and Irregular Galaxies
• Overview of Galaxy Structures
• The Local Group

Light Travel Time

• Galaxy Size and Luminosity
• Mass to Light Ratios
• Dark Matter in Galaxies
• Gravity of Many Bodies
• Galaxy Evolution
• Galaxy Interactions
• Galaxy Formation

Chapter 16 The Expanding Universe

• Galaxy Redshifts
• The Expanding Universe
• Cosmological Redshifts
• The Hubble Relation
• Relating Redshift and Distance
• Galaxy Distance Indicators
• Size and Age of the Universe
• The Hubble Constant
• Large Scale Structure
• Galaxy Clustering
• Clusters of Galaxies
• Overview of Large Scale Structure
• Dark Matter on the Largest Scales
• The Most Distant Galaxies
• Black Holes in Nearby Galaxies
• Active Galaxies
• Radio Galaxies
• The Discovery of Quasars
• Types of Gravitational Lensing
• Properties of Quasars
• The Quasar Power Source
• Quasars as Probes of the Universe
• Star Formation History of the Universe
• Expansion History of the Universe

Chapter 17 Cosmology

• Early Cosmologies
• Relativity and Cosmology
• The Big Bang Model
• The Cosmological Principle
• Universal Expansion
• Cosmic Nucleosynthesis
• Cosmic Microwave Background Radiation
• Discovery of the Microwave Background Radiation
• Measuring Space Curvature
• Cosmic Evolution
• Evolution of Structure
• Mean Cosmic Density
• Critical Density
• Dark Matter and Dark Energy
• Age of the Universe
• Precision Cosmology
• The Future of the Contents of the Universe
• Fate of the Universe
• Alternatives to the Big Bang Model
• Particles and Radiation
• The Very Early Universe
• Mass and Energy in the Early Universe
• Matter and Antimatter
• The Forces of Nature
• Fine-Tuning in Cosmology
• The Anthropic Principle in Cosmology
• String Theory and Cosmology
• The Multiverse
• The Limits of Knowledge

Chapter 18 Life On Earth

• Nature of Life
• Chemistry of Life
• Molecules of Life
• The Origin of Life on Earth
• Origin of Complex Molecules
• Miller-Urey Experiment
• Pre-RNA World
• From Molecules to Cells
• Extremophiles
• Thermophiles
• Psychrophiles
• Acidophiles
• Alkaliphiles
• Radiation Resistant Biology
• Importance of Water for Life
• Hydrothermal Systems
• Silicon Versus Carbon
• DNA and Heredity
• Life as Digital Information
• Synthetic Biology
• Life in a Computer
• Natural Selection
• Tree Of Life
• Evolution and Intelligence
• Culture and Technology
• The Gaia Hypothesis
• Life and the Cosmic Environment

Chapter 19 Life in the Universe

• Life in the Universe
• Astrobiology
• Life Beyond Earth
• Sites for Life
• Complex Molecules in Space
• Life in the Solar System
• Lowell and Canals on Mars
• Implications of Life on Mars
• Extreme Environments in the Solar System
• Rare Earth Hypothesis
• Are We Alone?
• Unidentified Flying Objects or UFOs
• The Search for Extraterrestrial Intelligence
• The Drake Equation
• The History of SETI
• Recent SETI Projects
• Recognizing a Message
• The Best Way to Communicate
• The Fermi Question
• The Anthropic Principle
• Where Are They?

In the everyday world, as perceived by the human senses, light seems to travel instantaneously from one place to another. In fact, the speed of light is not infinite, and light doesn't instantly jump from your ceiling light to your desk and then to your eye. We perceive light as moving instantly because its actual velocity is almost unimaginably high; light travels at 300,000 km/s, denoted c. Using the equation Rate × Time = Distance, you can divide any distance by this number to figure out the time it would take light to cross that distance. In this way, we can see that light takes 1.5 × 10 8 / 3 × 10 5 = 500 seconds to reach Earth from the Sun, or just over 8 minutes. It takes light about 40 times longer ( Pluto at a distance of 39.4 A.U.) to leave the Solar System or about 5 hours.

The speed of light is a built-in quality of our universe . All evidence to date indicates that light has always traveled at this speed, that the speed is exact, and that the same speed is observed for all observers. The vast size of the universe, coupled with the finite (albeit large) speed of light, means that as we look out in space, we look back in time. Distant light is old light.

The 5 hours it takes light to travel across our Solar System may seem like a short period to cross such a large distance, but we have to think about scale. While distances within the Solar System are large to us, they are dwarfed by the distances between the stars. Considering larger regions of the Milky Way, a natural distance unit is the distance light travels in one year. This is called a light year. We can easily calculate the size of this unit by remembering that distance has the units of velocity times time. So:

D ly = vt = c x 1 year = 3 × 10 5 x (3600 × 24 × 365) = 9.5 × 10 12 km

A light year is the typical distance between stars in the neighborhood of the Sun. It is nearly 10 trillion kilometers or 6 trillion miles! The fundamental unit of distance defined by geometry is the 13 km; defined as the distance corresponding to a parallax of 1 second of arc.">parsec , equal to 3.1 × 10 13 km. This is described in more detail in the article on parallax . Geometrically, one parsec is the height of a right triangle with an angle of 1 arcsec describing its apex , and a distance of 1 AU describing its base. The units are related by a small numerical constant D ly = 3.26 D pc . So to roughly convert from parsecs to light years, multiply by 3.3.

The following list gives the distance to various points within the Milky Way and beyond, both in terms of parsecs and the light travel time in years (which is also the distance in light years or 3.3 times the distance in parsecs). To fully appreciate how isolated we are in space, remember that light is the fastest thing we know of. The fastest spacecraft can not reach 1% of the speed of light. So you would have to multiply the numbers on the right-hand side of the table by at least 100 to estimate how long it would take to send a probe through the Milky Way and into the Local Group with current technology.

• Nearest star (α Centauri) - 1.3 pc, 4.2 years • Sirius - 2.7 pc, 8.8 years • Vega - 8.1 pc, 26 years • Hyades cluster - 42 pc, 134 years • Pleiades cluster - 125 pc, 411 years • Orion nebula - 460 pc, 1500 years • Nearest spiral arm - 1200 pc, 3900 years • Center of the 8 to 10 13 solar masses.">galaxy - 8500 pc, 29,000 years • Far edge of the galaxy - 24,000 pc, 78,000 years • Large Magellanic Cloud - 50,000 pc, 163,000 years • Andromeda galaxy (M31) - 670,000 pc, 2.2 million years

What does Andromeda look like now? Nobody knows. Since nothing travels faster than light (and this applies to all the colors of light across the electromagnetic spectrum ), there is no quicker way to send information from one place to another. We are stuck with collecting and measuring "old" light. While this seems like a limitation, scientists actually find that it turns out that light travel time is a wonderful tool. By looking further out in space we look further back in time. In this way, astronomers get to explore the earlier stages of the universe seeing firsthand (with a delay) what the early universe looked like.

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Three ways to travel at (nearly) the speed of light.

Katy Mersmann

1) electromagnetic fields, 2) magnetic explosions, 3) wave-particle interactions.

One hundred years ago today, on May 29, 1919, measurements of a solar eclipse offered verification for Einstein’s theory of general relativity. Even before that, Einstein had developed the theory of special relativity, which revolutionized the way we understand light. To this day, it provides guidance on understanding how particles move through space — a key area of research to keep spacecraft and astronauts safe from radiation.

The theory of special relativity showed that particles of light, photons, travel through a vacuum at a constant pace of 670,616,629 miles per hour — a speed that’s immensely difficult to achieve and impossible to surpass in that environment. Yet all across space, from black holes to our near-Earth environment, particles are, in fact, being accelerated to incredible speeds, some even reaching 99.9% the speed of light.

One of NASA’s jobs is to better understand how these particles are accelerated. Studying these superfast, or relativistic, particles can ultimately help protect missions exploring the solar system, traveling to the Moon, and they can teach us more about our galactic neighborhood: A well-aimed near-light-speed particle can trip onboard electronics and too many at once could have negative radiation effects on space-faring astronauts as they travel to the Moon — or beyond.

Here are three ways that acceleration happens.

Most of the processes that accelerate particles to relativistic speeds work with electromagnetic fields — the same force that keeps magnets on your fridge. The two components, electric and magnetic fields, like two sides of the same coin, work together to whisk particles at relativistic speeds throughout the universe.

In essence, electromagnetic fields accelerate charged particles because the particles feel a force in an electromagnetic field that pushes them along, similar to how gravity pulls at objects with mass. In the right conditions, electromagnetic fields can accelerate particles at near-light-speed.

On Earth, electric fields are often specifically harnessed on smaller scales to speed up particles in laboratories. Particle accelerators, like the Large Hadron Collider and Fermilab, use pulsed electromagnetic fields to accelerate charged particles up to 99.99999896% the speed of light. At these speeds, the particles can be smashed together to produce collisions with immense amounts of energy. This allows scientists to look for elementary particles and understand what the universe was like in the very first fractions of a second after the Big Bang. 

Download related video from NASA Goddard’s Scientific Visualization Studio

Magnetic fields are everywhere in space, encircling Earth and spanning the solar system. They even guide charged particles moving through space, which spiral around the fields.

When these magnetic fields run into each other, they can become tangled. When the tension between the crossed lines becomes too great, the lines explosively snap and realign in a process known as magnetic reconnection. The rapid change in a region’s magnetic field creates electric fields, which causes all the attendant charged particles to be flung away at high speeds. Scientists suspect magnetic reconnection is one way that particles — for example, the solar wind, which is the constant stream of charged particles from the Sun — is accelerated to relativistic speeds.

Those speedy particles also create a variety of side-effects near planets.  Magnetic reconnection occurs close to us at points where the Sun’s magnetic field pushes against Earth’s magnetosphere — its protective magnetic environment. When magnetic reconnection occurs on the side of Earth facing away from the Sun, the particles can be hurled into Earth’s upper atmosphere where they spark the auroras. Magnetic reconnection is also thought to be responsible around other planets like Jupiter and Saturn, though in slightly different ways.

NASA’s Magnetospheric Multiscale spacecraft were designed and built to focus on understanding all aspects of magnetic reconnection. Using four identical spacecraft, the mission flies around Earth to catch magnetic reconnection in action. The results of the analyzed data can help scientists understand particle acceleration at relativistic speeds around Earth and across the universe.

Particles can be accelerated by interactions with electromagnetic waves, called wave-particle interactions. When electromagnetic waves collide, their fields can become compressed. Charged particles bouncing back and forth between the waves can gain energy similar to a ball bouncing between two merging walls.

These types of interactions are constantly occurring in near-Earth space and are responsible for accelerating particles to speeds that can damage electronics on spacecraft and satellites in space. NASA missions, like the Van Allen Probes , help scientists understand wave-particle interactions.

Wave-particle interactions are also thought to be responsible for accelerating some cosmic rays that originate outside our solar system. After a supernova explosion, a hot, dense shell of compressed gas called a blast wave is ejected away from the stellar core. Filled with magnetic fields and charged particles, wave-particle interactions in these bubbles can launch high-energy cosmic rays at 99.6% the speed of light. Wave-particle interactions may also be partially responsible for accelerating the solar wind and cosmic rays from the Sun.

Download this and related videos in HD formats from NASA Goddard’s Scientific Visualization Studio

By Mara Johnson-Groh NASA’s Goddard Space Flight Center , Greenbelt, Md.

How Far is a Light Year?

How far is a light-year ? It might seem like a weird question because isn’t a ‘year’ a unit of time, and ‘far’ a unit of distance? While that is correct, a ‘light-year’ is actually a measure of distance. A light-year is the distance light can travel in one year.

Light is the fastest thing in our Universe traveling through interstellar space at 186,000 miles/second (300,000 km/sec). In one year, light can travel 5.88 trillion miles (9.46 trillion km).

A light year is a basic unit astronomers use to measure the vast distances in space.

To give you a great example of how far a light year actually is, it will take Voyager 1 (NASA’s longest-lived spacecraft) over 17,000 years to reach 1 light year in distance traveling at a speed of 61,000 kph.

Related Post: 13 Amazing Facts About Space

Why Do We Use Light-Years?

Because space is so vast, the measurements we use here on Earth are not very helpful and would result in enormous numbers.

When talking about locations in our own galaxy we would have numbers with over 18 zeros. Instead, astronomers use light-time measurements to measure vast distances in space. A light-time measurement is how far light can travel in a given increment of time.

• Light-minute: 11,160,000 miles
• Light-hour: 671 million miles
• Light-year: 5.88 trillion miles

Understanding Light-Years

To help wrap our heads around how to use light-years, let’s look at how far things are away from the Earth starting with our closest neighbor, the Moon.

The Moon is 1.3 light-seconds from the Earth.

Earth is about 8 light-minutes (~92 million miles) away from the Sun. This means light from the Sun takes 8 minutes to reach us.

Jupiter is approximately 35 light minutes from the Earth. This means if you shone a light from Earth it would take about a half hour for it to hit Jupiter.

Pluto is not the edge of our solar system, in fact, past Pluto, there is the Kieper Belt , and past this is the Oort Cloud . The Oort cloud is a spherical layer of icy objects surrounding our entire solar system.

If you could travel at the speed of light, it would take you 1.87 years to reach the edge of the Oort cloud. This means that our solar system is about 4 light-years across from edge to edge of the Oort Cloud.

The distance between the Sun and Interstellar Space. NASA/JPL-Caltech .

The nearest known exoplanet orbits the star Proxima Centauri , which is four light years away (~24 trillion miles). If a modern-day jet were to fly to this exoplanet it would not arrive for 5 million years.

One of the most distant exoplanets is 3,000 light-years (17.6 quadrillion miles) away from us in the Milky Way. If you were to travel at 60 miles an hour, you would not reach this exoplanet for 28 billion years.

Our Milky Way galaxy is approximately 100,000 light-years across (~588 quadrillion miles). Moving further into our Universe, our nearest neighbor, the Andromeda galaxy is 2.537 million light-years (14.7 quintillion miles) away from us.

The Andromeda Galaxy is 2.537 million light-years away from us.

Light, a Window into the Past

While we cannot actually travel through time, we can see into the past. How? We see objects because they either emit light or light has bounced off their surface and is traveling back to us.

Even though light is the fastest thing in our Universe, it takes time to reach us. This means that for any object we are seeing it how it was in the past. How far in the past? However long it took the light to reach us.

For day-to-day objects like a book or your dog, it takes a mere fraction of a fraction of a second for the light bouncing off the object to reach your eye. The further away an object is, the further into its past you are looking.

For instance, light from the Sun takes about 8 minutes to reach Earth, this means we are always seeing the Sun how it looked 8 minutes ago if you were on its surface.

The differences between Lunar Distance, an Astronomical Unit, and a Light Year. Illustration by Star Walk .

Traveling back through our solar system, Jupiter is approximately 30 light-minutes from Earth, so we see Jupiter how it looked 30 minutes ago if you were on its surface. Extending out into the Universe to our neighbor the Andromeda galaxy, we see it how it was 2.537 million years ago.

If there is another civilization out in the Universe watching Earth, they would not see us here today, they would see Earth in the past. A civilization that lives 65 million light-years away would see dinosaurs roaming the Earth.

Helpful Resources:

• How big is the Solar System? (Universe Today)
• What is an Astronomical Unit? (EarthSky)
• How close is Proxima Centauri? (NASA Imagine The Universe)

Convert Light Years to Kilometers

Search calculateme.

NASA Black Hole Visualization Takes Viewers Beyond the Brink

• Released Monday, May 6, 2024
• Produced by:
• Scott Wiessinger
• Written by:
• Francis Reddy
• Visualizations by:
• Jeremy Schnittman

In this flight toward a supermassive black hole, labels highlight many of the fascinating features produced by the effects of general relativity along the way. This supercomputer visualization tracks a camera as it approaches, briefly orbits, and then crosses the event horizon — the point of no return — of a supersized black hole similar in mass to the one at the center of our galaxy. Credit: NASA's Goddard Space Flight Center/J. Schnittman and B. PowellMusic: “Tidal Force,” Thomas Daniel Bellingham [PRS], Universal Production Music“Memories” from Digital Juice“Path Finder,” Eric Jacobsen [TONO] and Lorenzo Castellarin [BMI], Universal Production MusicWatch this video on the NASA Goddard YouTube channel.Complete transcript available.

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Complete transcript available.

• The outer edge of the accretion disk extends to a radius of about 97 million miles (156 million kilometers), comparable to the distance between Earth and the Sun.
• The inner edge of the accretion disk starts at a radius of around 23 million miles (38 million kilometers), about 25% of the Earth-Sun distance.
• The radius of the photon ring is 15.5 million miles (25 million kilometers).
• The event horizon radius is about 7.8 million miles (12.5 million kilometers).
• Spaghettification occurs around 79,500 miles (128,000 kilometers) from the singularity, the center of the black hole.

This version is encoded to play as a 360 VR movie. It follows the plunge of a simulated camera into a non-rotating supermassive black hole. The object's mass is 4.3 million Suns, equivalent to the black hole lying at the center of our Milky Way galaxy. The orange structure surrounding the black hole represents the hot, glowing gas of its accretion disk, where infalling matter collects and slowly spirals inward. Interior to the disk is a thin set of photon rings, which are images of the disk produced by light that has orbited the black hole one or more times before reaching the camera. The camera completes almost two orbits before hitting the event horizon. During the journey, a variety of effects caused by the gravitationally warped space-time around the black hole and the camera's speed become increasingly apparent. Images of the disk and the background sky morph, duplicate, and even form mirror images. Structures in the direction of travel, at the center of the simulation, brighten greatly as speed increases. At 42 seconds, the camera crosses the event horizon, traveling ever closer to the speed of light. Due to the camera’s speed, the entire sky appears to shift progressively forward, shrinking before our eyes. After entering the event horizon, the camera would be destroyed by tidal forces 12.8 seconds later, then in microseconds rush to the singularity, a point in the black hole's center where the laws of physics as we know them no longer apply.Credit: NASA's Goddard Space Flight Center/J. Schnittman and B. PowellMusic: “Tidal Force,” Thomas Daniel Bellingham [PRS], Universal Production MusicWatch this video on the NASA Goddard YouTube channel.Complete transcript available.

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Camera plunge, equidistant rectangular projection. This all-sky movie follows the plunge of a simulated camera into a non-rotating supermassive black hole. The object's mass is 4.3 million Suns, equivalent to the black hole lying at the center of our Milky Way galaxy. The orange structure surrounding the black hole represents the hot, glowing gas of its accretion disk, where infalling matter collects and slowly spirals inward. Interior to the disk is a thin set of photon rings, which are images of the disk produced by light that has orbited the black hole one or more times before reaching the camera. The camera completes almost two orbits before hitting the event horizon. During the journey, a variety of effects caused by the gravitationally warped space-time around the black hole and the camera's speed become increasingly apparent. Images of the disk and the background sky morph, duplicate, and even form mirror images. Structures in the direction of travel, at the center of the simulation, brighten greatly as speed increases. At 42 seconds, the camera crosses the event horizon, traveling ever closer to the speed of light. Due to the camera’s speed, the entire sky appears to shift progressively forward, shrinking before our eyes. After entering the event horizon, the camera would be destroyed by tidal forces 12.8 seconds later, then in microseconds rush to the singularity, a point in the black hole's center where the laws of physics as we know them no longer apply. Credit: NASA's Goddard Space Flight Center/J. Schnittman and B. Powell

• 14576_BH_Plunge_Rectilinear_8192x4096_60.mp4 [699.3 MB]
• 14576_BH_Plunge_Rectilinear_4096x2048_60.mp4 [349.7 MB]
• 14576_BH_Plunge_Rectilinear_2160x1080_30.mp4 [105.3 MB]
• 14576_BH_Plunge_Rectilinear_ProRes_8192x4096_60.mov [23.9 GB]
• Plunge_Rect [256.0 KB]
• Plunge_Rectilinear_Still_03528.jpg (8192x4096) [1.2 MB]

Credit: NASA's Goddard Space Flight Center/J. Schnittman and B. Powell

Camera plunge, Mollweide equal-area projection. This all-sky movie follows the plunge of a simulated camera into a non-rotating supermassive black hole. The object's mass is 4.3 million Suns, equivalent to the black hole lying at the center of our Milky Way galaxy. The orange structure surrounding the black hole represents the hot, glowing gas of its accretion disk, where infalling matter collects and slowly spirals inward. Interior to the disk is a thin set of photon rings, which are images of the disk produced by light that has orbited the black hole one or more times before reaching the camera. The camera completes almost two orbits before hitting the event horizon. During the journey, a variety of effects caused by the gravitationally warped space-time around the black hole and the camera's speed become increasingly apparent. Images of the disk and the background sky morph, duplicate, and even form mirror images. Structures in the direction of travel, at the center of the simulation, brighten greatly as speed increases. At 42 seconds, the camera crosses the event horizon, traveling ever closer to the speed of light. Due to the camera’s speed, the entire sky appears to shift progressively forward, shrinking before our eyes. After entering the event horizon, the camera would be destroyed by tidal forces 12.8 seconds later, then in microseconds rush to the singularity, a point in the black hole's center where the laws of physics as we know them no longer apply.Credit: NASA's Goddard Space Flight Center/J. Schnittman and B. Powell

• 14576_BH_Plunge_Mollweide_8192x4096_60.mp4 [699.0 MB]
• 14576_BH_Plunge_Mollweide_2160x1080_30.mp4 [105.5 MB]
• 14576_BH_Plunge_Mollweide_4096x2048_60.mp4 [349.7 MB]
• 14576_BH_Plunge_Mollweide_ProRes_8192x4096_60.mov [24.8 GB]
• Plunge_Moll [256.0 KB]
• Plunge_Mollweide_Still_02190.jpg (8192x4096) [3.5 MB]

This sequence shows a zoom into the plunging camera’s direction of travel to reveal the detailed structure of the photon rings. Each band is a distorted image of the gas disk layered between the background sky. Successive bands are thinner, produced by photons that have taken an additional trip around the black hole before reaching the camera. Due to the camera’s speed, which approaches 99.9% that of light toward the end, the entire sky appears to shift progressively forward, seemingly shrinking before our eyes. The field of view is 10 degrees across, about the width of a fist held at arm’s length. Credit: NASA's Goddard Space Flight Center/J. Schnittman and B. Powell

• 14576_BH_Plunge_Zoom2b_1080.mp4 [74.0 MB]
• 14576_BH_Plunge_Zoom_ProRes_3840x2160_60.mov [4.3 GB]
• 14576_BH_Plunge_Zoom2b_4k60.mp4 [241.0 MB]
• 14576_BH_Plunge_Zoom2b_ProRes_3840x2160_60.mov [4.1 GB]
• Plunge_Zoom [256.0 KB]
• Plunge_Zoom_Still_03607.jpg (3840x2160) [1.4 MB]

Plunge camera track. This movie tracks the position and orientation of the falling camera relative to the black hole. The inner circle represents the event horizon, the dashed circle represents the photon ring, which forms at the edge of the event horizon's shadow (twice the event horizon's size), and the dotted line shows the camera's path. A red line represents the plane of the accretion disk surrounding the black hole. At about 15 seconds, the image zooms in to follow the camera as it makes almost two loops around the black hole. At 42 seconds, the camera slips past the event horizon and arcs to the black hole's center.Credit: NASA's Goddard Space Flight Center/J. SchnittmanVisual description: On a black background, a white cartoon camera approaches a broken red line interrupted by a large dashed white circle at its center. Inside the dashed circle is a smaller white circle with a solid line. The camera, trailing a dotted line as it travels, spirals into the central white circle.

• 14576_BH_Plunge_Inset_900x480_60.mp4 [4.9 MB]
• 14576_BH_Plunge_Inset_ProRes_900x480_60.mov [153.1 MB]
• Plunge_Camera [256.0 KB]
• Plunge_Inset_Still_03170.jpg (900x480) [26.7 KB]

Visual description: On a black background, a white cartoon camera approaches a broken red line interrupted by a large dashed white circle at its center. Inside the dashed circle is a smaller white circle with a solid line. The camera, trailing a dotted line as it travels, spirals into the central white circle.

Plunge clock comparison. This movie tracks the local time of the falling camera, the time as experienced by a faraway observer (coordinate time), and the maximum blueshift observed. This is the factor by which the frequency of light in the direction of travel is increased. At 42 seconds, coordinate time reads all 9s, indicating that the camera has crossed the event horizon and external time is infinite. The blueshift continues to climb, exceeding 43 by the end, which indicates motion exceeding 99.9% light speed.Credit: NASA's Goddard Space Flight Center/J. SchnittmanVisual description: A box on a white background contains three lines of text. The top line reads "local time," the second line reads "coord time," and the third reads "max blueshift." As the video plays, these times increase and diverge as described above.

• 14576_BH_Plunge_Times_900x480_60.mp4 [15.8 MB]
• 14576_BH_Plunge_Times_ProRes_900x480_60.mov [154.5 MB]
• Plunge_Times [256.0 KB]
• Plunge_Times_Still_03900.jpg (900x480) [24.4 KB]

Visual description: A box on a white background contains three lines of text. The top line reads "local time," the second line reads "coord time," and the third reads "max blueshift." As the video plays, these times increase and diverge as described above.

In this flight toward a supermassive black hole, labels highlight many of the fascinating features produced by the effects of general relativity along the way. This supercomputer visualization tracks a camera as it approaches, falls toward, briefly orbits, and escapes a supersized black hole similar in mass to the one at the center of our galaxy. Credit: NASA's Goddard Space Flight Center/J. Schnittman and B. PowellMusic: "Beautiful Awesome,” David Husband and James William Banbury [PRS], Universal Production Music“Awakening Yearning,” David Ashok Ramani and Jonathan Elias [ASCAP], Universal Production Music“Dawning,” Lorenzo Castellarin [BMI], Universal Production MusicWatch this video on the NASA Goddard YouTube channel.Complete transcript available.

• 14576_BHFlyBy_Explainer_1080.mp4 [294.7 MB]
• 14576_BHFlyBy_Explainer_4k.mp4 [1.4 GB]
• 14576_BHFlyBy_Explainer_4kYouTube.mp4 [2.8 GB]
• 14576_BHFlyBy_Explainer_ProRes_3840x2160_2997.mov [12.9 GB]
• 14576_BHFlyBy_Explainer_Captions.en_US.srt [2.4 KB]
• 14576_BHFlyBy_Explainer_Captions.en_US.vtt [2.3 KB]
• 14576_BHFlyBy_Explain_Still.jpg (3840x2160) [1.1 MB]

This version is encoded to play as a 360 VR movie. It follows the trajectory of a simulated camera approaching and looping around a non-rotating supermassive black hole. The object's mass is 4.3 million Suns, equivalent to the black hole lying at the center of our Milky Way galaxy. The orange structure surrounding the black hole represents the hot, glowing gas of its accretion disk, where infalling matter collects and slowly spirals inward. Interior to the disk is a thin set of photon rings, which are images of the disk produced by light that has orbited the black hole one or more times before reaching the camera. The camera completes two orbits before escaping back out to safety. During the journey, a variety of effects caused by the gravitationally warped space-time around the black hole and the camera's speed become increasingly apparent. Images of the disk and the background sky morph, duplicate, and even form mirror images. Structures in the direction of travel, at the center of the simulation, brighten greatly as speed increases. At 46 seconds, the camera makes its closest approach to the event horizon, reaching maximum velocity at 60% the speed of light.Credit: NASA's Goddard Space Flight Center/J. Schnittman and B. PowellMusic: "Beautiful Awesome,” David Husband and James William Banbury [PRS], Universal Production MusicWatch this video on the NASA Goddard YouTube channel.Complete transcript available.

• 14576_BHFlyBy_360_FINAL_1080.mp4 [188.8 MB]
• 14576_BHFlyBy_360_FINAL_4k.mp4 [699.8 MB]
• 14576_BHFlyBy_360_FINAL_8k.mp4 [1.4 GB]
• 14576_BHFlyBy_360VR_FINAL_8k.mp4 [1.4 GB]
• 14576_BHFlyBy_360VR_FINAL_4k.mp4 [699.8 MB]
• 14576_BHFlyBy_360VR_FINAL_1080.mp4 [188.9 MB]
• 14576_BHFlyBy_360_Captions.en_US.srt [213 bytes]
• 14576_BHFlyBy_360_Captions.en_US.vtt [213 bytes]
• 14576_BHFlyBy_360_Still.jpg (3840x2160) [1.1 MB]

Camera flyby, equidistant rectangular projection. This all-sky movie follows the trajectory of a simulated camera approaching and orbiting a non-rotating supermassive black hole. The object's mass is 4.3 million Suns, equivalent to the black hole lying at the center of our Milky Way galaxy. The orange structure surrounding the black hole represents the hot, glowing gas of its accretion disk, where infalling matter collects and slowly spirals inward. Interior to the disk is a thin set of photon rings, which are images of the disk produced by light that has orbited the black hole one or more times before reaching the camera. The camera completes two orbits before escaping back out to safety. During the journey, a variety of effects caused by the gravitationally warped space-time around the black hole and the camera's speed become increasingly apparent. Images of the disk and the background sky morph, duplicate, and even form mirror images. Structures in the direction of travel, at the center of the simulation, brighten greatly as speed increases. At 46 seconds, the camera makes its closest approach to the event horizon, reaching maximum velocity at 60% the speed of light. Credit: NASA's Goddard Space Flight Center/J. Schnittman and B. Powell

• 14576_BH_FlyBy_Rectilinear_2160x1080_30.mp4 [118.4 MB]
• 14576_BH_FlyBy_Rectilinear_4096x2048_60.mp4 [395.0 MB]
• 14576_BH_FlyBy_Rectilinear_8192x4096_60.mp4 [789.8 MB]
• 14576_BH_FlyBy_Rectilinear_ProRes_8192x4096_60.mov [33.3 GB]
• FlyBy_Rect [256.0 KB]
• FlyBy_Rectilinear_01787.jpg (8192x4096) [3.9 MB]

Camera flyby, Mollweide equal-area projection. This all-sky movie follows the trajectory of a simulated camera approaching and orbiting a non-rotating supermassive black hole. The object's mass is 4.3 million Suns, equivalent to the black hole lying at the center of our Milky Way galaxy. The orange structure surrounding the black hole represents the hot, glowing gas of its accretion disk, where infalling matter collects and slowly spirals inward. Interior to the disk is a thin set of photon rings, which are images of the disk produced by light that has orbited the black hole one or more times before reaching the camera. The camera completes two orbits before escaping back out to safety. During the journey, a variety of effects caused by the gravitationally warped space-time around the black hole and the camera's speed become increasingly apparent. Images of the disk and the background sky morph, duplicate, and even form mirror images. Structures in the direction of travel, at the center of the simulation, brighten greatly as speed increases. At 46 seconds, the camera makes its closest approach to the event horizon, reaching maximum velocity at 60% the speed of light. Credit: NASA's Goddard Space Flight Center/J. Schnittman and B. Powell

• 14576_BH_FlyBy_Mollweide_ProRes_8192x4096_60.mov [35.8 GB]
• 14576_BH_FlyBy_Mollweide_4096x2048_60.mp4 [395.1 MB]
• 14576_BH_FlyBy_Mollweide_8192x4096_60.mp4 [789.8 MB]
• FlyBy_Moll [256.0 KB]
• FlyBy_Mollweide_Still_01830.jpg (8192x4096) [3.6 MB]

This sequence shows a zoom into the camera’s direction of travel as it loops around the black hole to reveal the detailed structure of the photon rings. Each band is a distorted image of the gas disk layered between the background sky. Successive bands are thinner, produced by photons that have taken an additional trip around the black hole before reaching the camera. The field of view is 10 degrees across, about the width of a fist held at arm’s length. Credit: NASA's Goddard Space Flight Center/J. Schnittman and B. Powell

• 14576_BH_FlyBy_Zoom2_1920x1080_30.mp4 [78.6 MB]
• 14576_BH_FlyBy_Zoom2_3840x2160_60.mp4 [196.6 MB]
• 14576_BH_FlyBy_Zoom2_ProRes_3840x2160_60.mov [3.0 GB]
• FlyBy_Zoom [128.0 KB]
• FlyBy_Zoom_Still_01650.jpg (3840x2160) [914.1 KB]

Flyby camera track. This movie tracks the position and orientation of the falling camera relative to the black hole. The inner circle represents the event horizon, the dashed circle represents the photon ring, which forms at the edge of the event horizon's shadow (twice the event horizon's size), and At about 15 seconds, the image zooms in to follow the camera as it makes two loops around the black hole. At 46 seconds, the image zooms out as the camera escapes. Credit: NASA's Goddard Space Flight Center/J. SchnittmanVisual description: On a black background, a white cartoon camera approaches a broken red line interrupted by a large dashed white circle at its center. Inside the dashed circle is a smaller white circle with a solid line. The camera, trailing a dotted line as it travels, loops twice around the dashed circle.

• 14576_BH_FlyBy_Inset_900x480_60.mp4 [8.6 MB]
• 14576_BH_FlyBy_Inset_ProRes_900x480_60.mov [143.7 MB]
• FlyBy_Camera [256.0 KB]
• FlyBy_Inset_Still_03126.jpg (900x480) [26.5 KB]

Visual description: On a black background, a white cartoon camera approaches a broken red line interrupted by a large dashed white circle at its center. Inside the dashed circle is a smaller white circle with a solid line. The camera, trailing a dotted line as it travels, loops twice around the dashed circle.

Flyby clock comparison. This movie tracks the local time of the falling camera, the time as experienced by a faraway observer (coordinate time), and the maximum blueshift observed. This is the factor by which the frequency of light in the direction of travel is increased. As the video plays, these times increase and diverge, and by the end, local time lags coordinate time by 36 minutes. At 46 seconds, the blueshift reaches 2.34 as the camera's motion peaks at 60% the speed of light.Credit: NASA's Goddard Space Flight Center/J. SchnittmanVisual description: A box on a white background contains three lines of text. The top line reads "local time," the second line reads "coord time," and the third reads "max blueshift."

• 14576_BH_FlyBy_Timess_900x480_60.mp4 [22.3 MB]
• 14576_BH_FlyBy_Times_ProRes_900x480_60.mov [172.6 MB]
• FlyBy_Times [256.0 KB]
• FlyBy_Times_Still_04360.jpg (900x480) [23.6 KB]

Visual description: A box on a white background contains three lines of text. The top line reads "local time," the second line reads "coord time," and the third reads "max blueshift."

For More Information

See NASA.gov

• Astrophysics
• Supercomputer
• Supermassive Black Hole
• Visualization

Please give credit for this item to: NASA's Goddard Space Flight Center. However, individual items should be credited as indicated above.

• Scott Wiessinger  (KBR Wyle Services, LLC)

Science writer

• Francis Reddy  (University of Maryland College Park)
• Jeremy Schnittman  (NASA/GSFC)
• Brian Powell  (NASA/GSFC)
• Ernie Wright  (USRA)

Release date

This page was originally published on Monday, May 6, 2024. This page was last updated on Monday, May 6, 2024 at 4:04 PM EDT.

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Beyond the Brink: Tracking a Simulated Plunge into a Black Hole

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Northern lights could be visible in Delaware tonight as 'severe' solar storm predicted

Have you always wanted to see the northern lights but never been able to travel far enough north to catch a glimpse?

There's a chance they could be visible from Delaware and nearby states Friday night.

Over the last several days, space weather forecasters have been closely monitoring the sun following a series of solar flares and coronal mass ejections. These are explosions of plasma and magnetic fields, which cause geomagnetic storms.

On Earth, the storms can cause disruptions in communications, the electric power grid, navigation and radio. In space, they can affect satellites.

But the storms can also trigger "spectacular displays" of the northern lights, or aurora borealis, according to NOAA's Space Weather Prediction Center . A "severe" storm means the aurora could be seen as far south as Alabama and northern California.

This would also include Delaware.

The last time space weather forecasters issued a severe (G4) geomagnetic storm watch − the second most powerful solar storm classification − was January 2005, though a G4 storm did occur in March of this year.

A G5 storm is the most severe and classified as "extreme." The last one occurred in October 2003 and caused power outages in Sweden. It also damaged power transformers in South Africa, according to the Space Weather Prediction Center .

When could I see the northern lights?

Timing is not exact, but the time to view the aurora is usually within several hours of midnight, or between 10 p.m. and 2 a.m. local time. There can be aurora in the evening and morning, but it is not usually as active, according to NOAA.

During a Friday morning news conference, officials with the space weather prediction center said they will not know the intensity of the storm until the coronal mass ejections reach about a million miles from Earth. They travel at 800 kilometers (497 miles) per second, meaning scientists will have 20 to 45 minutes to determine the intensity before any potential effects are felt or seen.

"Because we're talking about something (that originates) 93 million miles away, it is extremely difficult to forecast with a very good degree of accuracy," said Shawn Dahl, a service coordinator with the space weather prediction center.

But, he and others added, if the solar storm does reach the G4 level, sky gazers should look up in the "late evening to post-midnight hours."

For best viewing, the National Weather Service recommends looking to the north and trying to get away from city lights. The darker the sky, the better for viewing, weather officials say.

While Friday night appears to be the best chance for viewing, the aurora may also be visible Saturday night into Sunday.

Will Friday's rain affect my potential viewing?

One key requirement to seeing the aurora is clear skies − meaning Friday's wet weather may hinder potential viewing.

Rain is expected to continue on and off throughout much of the day in Delaware, though radar shows it tapering off around 9 p.m.

WEEKEND WEATHER: Grab your raincoats, Delaware. It's going to be a dreary weekend with rain, cloudy skies

Still, cloud cover is predicted at 100% at 10 p.m., 98% at 11 p.m., 98% at midnight, 97% at 1 a.m. and 93% at 2 a.m., according to the National Weather Service .

While Delaware will likely have an overnight reprieve from rain, a frontal system developing over the Midwest will cause precipitation to return to the Mid-Atlantic on Saturday with another round of rain and thunderstorms.

The storm will be weaker than Friday's, however, and severe thunderstorms are not expected, the weather service said.

What are the northern lights? 

The aurora borealis is a glow produced by electrons that float down to the Earth’s magnetic field from space.  The electrons crash with atoms and molecules of the atmosphere in a ring on the Earth’s magnetic pole,  according to NOAA . 

All that commotion produces multicolor bulbs of light, which can be seen in the Northern and Southern hemispheres, respectively.  

Got a story tip or idea? Send to Isabel Hughes at [email protected]. For all things breaking news, follow her on X at @izzihughes_

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Travel Light With the 15 Best Sleek and Stylish Crossbody Purses, Sling Bags, and More — From $14

Handpicked by someone who hates traveling with a big bag.

Travel + Leisure / Tyler Roeland

No matter the destination, traveling can be an amazing experience, and having the right purse can make your life on the road smoother. But what if you’re someone who doesn’t love carrying a big bag as you stroll through a farmer’s market in Seattle or hike Rocky Mountain National Park? 

Don’t worry, we’ve got plenty of suggestions for you. These days, large purses are far from a necessity. We found 15 travel purses and bags that will hold everything you need without weighing you down — and they’ll fit right into an overhead bin or under the seat if you’re flying. That's not even the best part: These top-rated styles, ranging from sleek sling bags and belt bags to RFID-blocking crossbody purses and backpacks , start at just $14.  

Kedzie Quilted Puffer Crossbody Bag

This convertible sling bag from Kedzie has become my go-to travel purse. The zippered front pocket is perfect for lip gloss and receipts while the larger two zippered pockets hold lotion, wallet, phone, gum, and more. You can wear this like a crossbody or over your shoulder, plus, a second strap is included if you want to wear it like a backpack. 

Reviewers have said they want to buy multiples after trying the bag. They have also called it the “perfect size” that " holds everything I need and more ."

Everlane The Recycled Nylon Camera Bag

Yes, this is a camera bag, and you can absolutely carry a camera in it. But it’s good for so much more than that with its adjustable crossbody style strap, two zippered compartments, and an exterior slip pocket. The main body is made with 100 percent recycled nylon while the lining is 100 percent recycled polyester. Tasteful neutrals like black, khaki, and beige will go with anything — saving you precious luggage space.

“It's a great size with enough room for the essentials; it holds my wallet (not a small one), keys, phone, glasses, lipstick,” raved one reviewer. “I love it so much I bought it in two colors.”

Everlane The Cactus Leather Sling Bag

Sling bags are in, and this option brings sophisticated vibes for a girls’ weekend in wine country. Made with organically sourced prickly pear cactus (who knew?), the brand's Desserto material is a fabulous leather alternative. No digging in the bottomless abyss of a giant purse here — it’s got just enough room for just the basics, like a card or two, lip balm, and your phone. Choose from sleek cashew, dark honey, or day-brightening lime green.

“I am also a bare necessity type of girl, so I love the fact that it really only fits my small wallet, phone, and chapstick," one shopper was happy to report. "It will be wonderful for travel as well with a passport." 

Patagonia Atom Sling Bag

If you’ve got active travel plans like exploring the Grand Canyon, you’ll want to grab this sling bag from Patagonia. The four color options include two solid hues and two vibrantly color-blocked options, all of which are water-repellant, made with recycled materials, and Fair Trade Certified sewn. Weighing just 12 ounces, it has an impressive capacity of 488 cubic inches with a phone pocket and two main compartments. You can even use it to bring your yoga mat along by using the tuckaway front straps. Now those are Namaste vibes!

According to one reviewer, who hiked not one but two challenges (100 miles in 100 days each), said, “I can always fit more than I think in the outermost compartment. The mesh pocket holds {my} phone perfectly, and it's easy to access everything even when the bag is on.”

Osprey Daylite Pack

Want something slightly larger than a sling bag? This backpack weighs just over 1 pound and can fit a 13-inch laptop in its roomy, three-compartment interior. Its compact size makes it an ideal personal item if you’re flying to your next workcation since it’ll fit right under the airplane seat. You’ll stay hydrated with two side pockets for water bottles and you can keep your keys close by with the attached key clip. Plus, the four solid jewel-tone hues lend just the right amount of understated style. 

From hikes to flights, reviewers love this bag for any adventure. One chimed in, “This was perfect for my flight excursion. It's just the right size and shape, [and is] lightweight and comfortable.”

Fjallraven High Coast Crossbody Bag

This crossbody may look like your average purse, but it has a detachable strap that turns the bag into a sleek pouch when you're on the go. It has two main compartments, a key hook, and two interior mesh sleeves to keep everything in its place, whether used as a cosmetics pouch in your checked bag or as a purse while dashing to your airport gate. It's available in olive green and black hues, and both styles are just $50.

Though it's perfect for travel, reviewers love that it makes for a great everyday bag. One REI customer said, “This bag does the tricks great for travel, hiking, [and] dinner out with friends. It holds way more than you think, and the outside pocket is a nice added bonus." 

Baggallini Crossbody Bag With RFID-blocking Wristlet

Known for functionality and plenty of pockets, Baggallini crossbody bags live up to the brand’s reputation. Five colors are available, including black and a fun lipstick red. The bag has RFID-blocking protection in the included wristlet for peace of mind while jet-setting, plus three exterior zip pockets. It’ll stow nicely under an airplane seat and you can even machine wash the bag. Bonus: It’s on sale starting at $49 — the lowest price we’ve seen in a month.

“The size is perfect [and has] enough space to fit everything: keys, glasses (two pairs), a wallet, a phone, [and more] odds and ends," a reviewer described. "[There are] zippers to keep everything in securely and just enough compartments to organize." 

Arc’teryx Mantis 1 Waist Pack

Into hands-free travel bags? Arc’teryx’s waist pack has a rugged appeal and can be worn around the waist or over your shoulder. At 15 inches wide, the two zippered compartments hold a respectable amount of goods, including your keys with its interior key clip. The Yukon hue is a medium tan and the bag is made from recycled poly material for a durable yet environmentally friendly option that’s less than $50.

Taking to the review section, a traveler explained how useful it is as both a travel and an everyday bag, saying, “While traveling, it was great that it could hold larger portable batteries for phones, wallets, snack bars, keys, coins, etc. The zippers are very robust and zip very smoothly.”

Frye Melissa Zip Crossbody

Frye is known for quality leather bags, but with this on-sale option, the brand is bringing in a little shimmer for those who can’t say no to a bit of glam. The three hues include denim blue, oatmeal beige, and dusty rose to match your favorite travel outfits. It has a zippered main compartment with an interior pocket, as well as an outer slip pocket and an adjustable strap. 

Reviewers adore this bag and rave that it’s “roomy” yet lightweight. Another happy shopper said even when the bag is full, it still has a slim profile. 

Dagne Dover Mara Phone Sling Crossbody Bag

If you’re gifted with the elusive (for me, anyway) skill of packing light, you’ll want to grab this Dagne Dover phone sling bag. It has a crossbody strap that can go from 14.5 to 28 inches, and the bag itself measures just 6.5 inches wide — just enough room for your phone, a lip balm, and a credit card or a bit of cash. You have four colors to choose from, like classic black or a deep moss green. 

“I take this literally everywhere with me and have two young kids. It's much easier to fish things out [of] this than any giant bag of kid stuff,” said one clever reviewer. “And it’s trendy and cute when I’m without kiddos.”

Hobo Draft Leather Crossbody Bag

This bag will be your new best friend if you appreciate versatility and a timeless style. Available in all neutral colors (black, white, or tan), it has an adjustable strap that you can remove to transform the bag into a clutch for a night out. The foldover flap gives it extra style while upping its content's protection, and the luxe leather material elevates it into a chic everyday bag.

Reviewers say the bag is soft and holds plenty of items without bulging. One shopper noted it was “perfect” for carrying a wallet and passport during their international travels. 

Madewell The Essential Mini Bucket Tote

It’s possible to get the style of a bucket bag without the bulk thanks to Madewell. Measuring just 8.5 inches tall, this bag can be worn as a crossbody or shoulder bag. Plus, it’s structured like a classic bucket bag and has a flat base to keep it upright for easy packing and tracking down what you need inside. The elegant leather bag also comes in a warm brown or a beige hue for a timeless look.

Multiple reviewers have called it a “great bag,” with some calling it the “perfect size.” And it currently has a perfect five-star rating from all reviewers at Nordstrom.  

Travelon Women’s Messenger Bag

Have travel plans to busy destinations? Check out Travelon’s anti-theft messenger bag for peace of mind, especially while weaving through crowded stadiums or venues. Its five-point anti-theft features (like a slash-resistant material) make it a smart choice while the front magnetic flap adds style and an obstacle for thieves and pickpockets. Keep your water bottle handy in the side pocket and stash your passport and other important documents in one of many zippered or slip pockets. The classic black version is $80, but select colors (like olive green) are on sale for as little as $51.

It’s easy to see why over 6,200 people have given it a perfect five-star rating. One traveler , who bought multiples, said, “It has excellent security features. All [the] zippers have clasps that secure them. There is a front pocket that works great for cell phone, on the opposite side, one outside pocket that works great for credit cards, passport, etc., and has RFID protection.”

Bostanten Small Phone Crossbody Bag

Available in an impressive 15 colors and patterns, this vegan leather cell phone bag can hold four cards plus a phone, along with some small essentials in the zippered pockets. The crossbody strap is adjustable, but you can remove it and slip this small bag into a larger one if you need more supplies for all-day sightseeing excursions. 

“I purchased this for a Caribbean cruise vacation; I fit three passports, credit cards, a driver's license, a hotel keycard, car keys, and a ship sea pass, and still had room for lipstick, a folded excursion map, receipts, and other essentials,” one cruise goer shared . “I’m glad I bought it.”

Maxtop Fanny Pack

Last but not least, this fanny pack is another perfect travel companion if you don’t want to carry around a huge bag. It’s just $14 (but currently on sale for $9) and comes in four colors (black, two gray hues, and pink). Within the zippered main compartment, there’s a hidden pocket to store your cash or passport. Wear it as a classic fanny pack (the ‘90s are back, after all!) or as a sling. 

“I bought this cross-shoulder bag for vacation and wanted a nice looking, comfortable cross-shoulder bag that carried just what I needed — that’s what I got,” exclaimed one shopper . Another traveler added , “It feels good worn in the traditional sense, but I do prefer the strap across the shoulders.”

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