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What Is a Light-Year?

An image of hundreds of small galaxies on the black background of space.

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.

A chart explaining how far away certain objects are from Earth. The Sun is 8.3 light-minutes away. Polaris is 320 light-years away. Andromeda is 2.5 million light years away. Proxima Centauri is 4.3 light-years away. The center of the Milky Way is 26,000 light-years away. GN-z11 is 13.4 billion 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, which appears as a blue and white swirling mass among hundreds more galaxies in the background.

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.

Picture of hundreds of galaxies with one shown zoomed in to see greater detail. The zoomed in part looks like a red blob.

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)

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FREQUENTLY ASKED QUESTIONS

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-443b. Traveling at light speed, it would take 3,000 years to get there. Or 28 billion years, going 60 mph.

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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.

Distance between Sun and Earth

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.

Andromeda Galaxy at 105mm

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.

astronomical unit

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)
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  • NGC 1097 (Spitzer)
  • Helix (Spitzer)
  • Flame Nebula (WISE)
  • Galactic Center (2MASS)
  • Cool Andromeda (Herschel)

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Space Terms

  • What is a satellite?
  • What is an Astronomical Unit?
  • What is gravity?
  • What does escape velocity mean?
  • What is absolute zero?

What is a light-year?

The fastest thing that we know of is light which travels at a speed of 186,000 miles or 300,000 kilometers per second in empty space. To get an idea of how fast this is, light can travel about seven times around Earth in one second! Astronomers use the speed of light to measure how far away things are in space. A light-year (ly) is the distance that light can travel in one year. In one year, light travels about 5,880,000,000,000 miles or 9,460,000,000,000 kilometers. So, this distance is 1 light-year. For example, the nearest star to us is about 4.3 light-years away. Our galaxy, the Milky Way, is about 150,000 light-years across, and the nearest large galaxy, Andromeda, is 2.3 million light-years away.

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What is the speed of light?

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

graphic representing the speed of light showing lines of light of different colors; blue, green, yellow and white.

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, 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

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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Cosmic Distances

The trinary star Alpha Centauri, hangs above the horizon of Saturn

The space beyond Earth is so incredibly vast that units of measure which are convenient for us in our everyday lives can become GIGANTIC. Distances between the planets, and especially between the stars, can become so big when expressed in miles and kilometers that they're unwieldy. So for cosmic distances, we switch to whole other types of units: astronomical units, light years and parsecs.

Astronomical units, abbreviated AU, are a useful unit of measure within our solar system. One AU is the distance from the Sun to Earth's orbit, which is about 93 million miles (150 million kilometers). When measured in astronomical units, the 886,000,000-mile (1,400,000,000-kilometer) distance from the Sun to Saturn's orbit, is a much more manageable 9.5 AU. So astronomical units are a great way to compress truly astronomical numbers to a more manageable size.

Astronomical units also make it easy to think about distances between solar system objects. They make it easy to see that Jupiter orbits five times farther from the Sun than Earth, and that Saturn is twice as far from the Sun as Jupiter. (This is because, technically, you're expressing every distance as a ratio of the distance from Earth to the Sun. Convenient!)

For much greater distances — interstellar distances — astronomers use light years. A light year is the distance a photon of light travels in one year, which is about 6 trillion miles (9 trillion kilometers, or 63,000 AU). Put another way, a light year is how far you'd travel in a year if you could travel at the speed of light, which is 186,000 miles (300,000 kilometers) per second. (By the way, you can't travel at the speed of light, as far as we know, but that's a whole other story...) Like AU, light years make astronomical distances more manageable. For example, the nearest star system to ours is the triple star system of Alpha Centauri , at about 4.3 light years away. That's a more manageable number than 25 trillion miles, 40 trillion kilometers or 272,000 AU.

Light years also provide some helpful perspective on solar system distances: the Sun is about 8 light minutes from Earth. (And yes, there are also light seconds !) And because light from objects travels at light speed , when you see the Sun, or Jupiter or a distant star, you're seeing it as it was when the light left it, be that 8 minutes, tens of minutes or 4.3 years ago. And this is fundamental to the idea that when we're looking farther out into space, we're seeing farther back in time. (Think about it: you're seeing all the stars in the sky at different times in history — some a few years ago, others hundreds of years ago — all at the same time!)

Finally, parsecs. This is the unit used when the number of light years between objects climbs into the high thousands or millions. One parsec is 3.26 light years. The origin of this unit of measure is a little more complicated, but it's related to how astronomers measure widths in the sky. Astronomers use "megaparsecs" — a megaparsec is 1 million parsecs — for intergalactic distances, or the scale of distances between the galaxies.

And at the point when distances between galaxies become so epic that even megaparsecs get unwieldy, astronomers talk about distances in terms of how much a galaxy's light has been shifted toward longer, redder wavelengths by the expansion of the universe — a measure known as "redshift." Now that's astronomical.

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How Long Would It Take To Travel A Light Year

light travel in a year

Using the fastest man-made vehicle, NASA’s Juno spacecraft, which travels at 165,000 mph (365,000 kmph), it would take 2,958 years to travel a light year. A light year is equivalent to about 5.88 trillion miles (9.46 trillion kilometers).

Traveling at the speed of light would be the fastest way to cover vast distances in space, but current technology makes it impossible for humans or even our most advanced spacecraft to reach this speed.

Can people match the speed of a light year?

According to Einstein, it is impossible to match the speed of light. It is because light is the fastest thing in the universe, traveling at 186,000 miles per second (300,000 kilometers per second). There is not one thing that we could invent that could even match a fraction of how fast light travels.

Some scientists have theorized that a new type of engine, called a warp drive , could potentially allow humans to reach the speed of travel required to match the speed of light. However, even if future spacecrafts were able to achieve this level of propulsion, it would still take thousands of years to travel from one star system to another.

Despite the challenges, scientists continue to study space travel at faster-than-light speeds, as they are optimistic that one day we will be able to explore the vast reaches of our universe and even discover life on other planets.

For now, it would take many thousands of years to travel a light year using current technology. However, scientists remain hopeful that one day we will be able to explore the far reaches of space and perhaps even discover other life forms in distant star systems. Until then, we can continue marveling at the

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What is the speed of light? Here’s the history, discovery of the cosmic speed limit

Time travel is one of the most intriguing topics in science.

On one hand, the speed of light is just a number: 299,792,458 meters per second. And on the other, it’s one of the most important constants that appears in nature and defines the relationship of causality itself.

As far as we can measure, it is a constant. It is the same speed for every observer in the entire universe. This constancy was first established in the late 1800’s with the experiments of Albert Michelson and Edward Morley at Case Western Reserve University . They attempted to measure changes in the speed of light as the Earth orbited around the Sun. They found no such variation, and no experiment ever since then has either.

Observations of the cosmic microwave background, the light released when the universe was 380,000 years old, show that the speed of light hasn’t measurably changed in over 13.8 billion years.

In fact, we now define the speed of light to be a constant, with a precise speed of 299,792,458 meters per second. While it remains a remote possibility in deeply theoretical physics that light may not be a constant, for all known purposes it is a constant, so it’s better to just define it and move on with life.

How was the speed of light first measured?

In 1676 the Danish astronomer Ole Christensen Romer made the first quantitative measurement of how fast light travels. He carefully observed the orbit of Io, the innermost moon of Jupiter. As the Earth circles the Sun in its own orbit, sometimes it approaches Jupiter and sometimes it recedes away from it. When the Earth is approaching Jupiter, the path that light has to travel from Io is shorter than when the Earth is receding away from Jupiter. By carefully measuring the changes to Io’s orbital period, Romer calculated a speed of light of around 220,000 kilometers per second.

Observations continued to improve until by the 19 th century astronomers and physicists had developed the sophistication to get very close to the modern value. In 1865, James Clerk Maxwell made a remarkable discovery. He was investigating the properties of electricity and magnetism, which for decades had remained mysterious in unconnected laboratory experiments around the world. Maxwell found that electricity and magnetism were really two sides of the same coin, both manifestations of a single electromagnetic force.

James Clerk Maxwell contributed greatly to the discover of the speed of light.

As Maxwell explored the consequences of his new theory, he found that changing magnetic fields can lead to changing electric fields, which then lead to a new round of changing magnetic fields. The fields leapfrog over each other and can even travel through empty space. When Maxwell went to calculate the speed of these electromagnetic waves, he was surprised to see the speed of light pop out – the first theoretical calculation of this important number.

What is the most precise measurement of the speed of light?

Because it is defined to be a constant, there’s no need to measure it further. The number we’ve defined is it, with no uncertainty, no error bars. It’s done. But the speed of light is just that – a speed. The number we choose to represent it depends on the units we use: kilometers versus miles, seconds versus hours, and so on. In fact, physicists commonly just set the speed of light to be 1 to make their calculations easier. So instead of trying to measure the speed light travels, physicists turn to more precisely measuring other units, like the length of the meter or the duration of the second. In other words, the defined value of the speed of light is used to establish the length of other units like the meter.

How does light slow down?

Yes, the speed of light is always a constant. But it slows down whenever it travels through a medium like air or water. How does this work? There are a few different ways to present an answer to this question, depending on whether you prefer a particle-like picture or a wave-like picture.

In a particle-like picture, light is made of tiny little bullets called photons. All those photons always travel at the speed of light, but as light passes through a medium those photons get all tangled up, bouncing around among all the molecules of the medium. This slows down the overall propagation of light, because it takes more time for the group of photons to make it through.

In a wave-like picture, light is made of electromagnetic waves. When these waves pass through a medium, they get all the charged particles in motion, which in turn generate new electromagnetic waves of their own. These interfere with the original light, forcing it to slow down as it passes through.

Either way, light always travels at the same speed, but matter can interfere with its travel, making it slow down.

Why is the speed of light important?

The speed of light is important because it’s about way more than, well, the speed of light. In the early 1900’s Einstein realized just how special this speed is. The old physics, dominated by the work of Isaac Newton, said that the universe had a fixed reference frame from which we could measure all motion. This is why Michelson and Morley went looking for changes in the speed, because it should change depending on our point of view. But their experiments showed that the speed was always constant, so what gives?

Einstein decided to take this experiment at face value. He assumed that the speed of light is a true, fundamental constant. No matter where you are, no matter how fast you’re moving, you’ll always see the same speed.

This is wild to think about. If you’re traveling at 99% the speed of light and turn on a flashlight, the beam will race ahead of you at…exactly the speed of light, no more, no less. If you’re coming from the opposite direction, you’ll still also measure the exact same speed.

This constancy forms the basis of Einstein’s special theory of relativity, which tells us that while all motion is relative – different observers won’t always agree on the length of measurements or the duration of events – some things are truly universal, like the speed of light.

Can you go faster than light speed?

Nope. Nothing can. Any particle with zero mass must travel at light speed. But anything with mass (which is most of the universe) cannot. The problem is relativity. The faster you go, the more energy you have. But we know from Einstein’s relativity that energy and mass are the same thing. So the more energy you have, the more mass you have, which makes it harder for you to go even faster. You can get as close as you want to the speed of light, but to actually crack that barrier takes an infinite amount of energy. So don’t even try.

How is the speed at which light travels related to causality?

If you think you can find a cheat to get around the limitations of light speed, then I need to tell you about its role in special relativity. You see, it’s not just about light. It just so happens that light travels at this special speed, and it was the first thing we discovered to travel at this speed. So it could have had another name. Indeed, a better name for this speed might be “the speed of time.”

Related: Is time travel possible? An astrophysicist explains

We live in a universe of causes and effects. All effects are preceded by a cause, and all causes lead to effects. The speed of light limits how quickly causes can lead to effects. Because it’s a maximum speed limit for any motion or interaction, in a given amount of time there’s a limit to what I can influence. If I want to tap you on the shoulder and you’re right next to me, I can do it right away. But if you’re on the other side of the planet, I have to travel there first. The motion of me traveling to you is limited by the speed of light, so that sets how quickly I can tap you on the shoulder – the speed light travels dictates how quickly a single cause can create an effect.

The ability to go faster than light would allow effects to happen before their causes. In essence, time travel into the past would be possible with faster-than-light travel. Since we view time as the unbroken chain of causes and effects going from the past to the future, breaking the speed of light would break causality, which would seriously undermine our sense of the forward motion of time.

Why does light travel at this speed?

No clue. It appears to us as a fundamental constant of nature. We have no theory of physics that explains its existence or why it has the value that it does. We hope that a future understanding of nature will provide this explanation, but right now all investigations are purely theoretical. For now, we just have to take it as a given.

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What Is a Light-year?

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A blue and purple cosmic view of the stars.

A light-year is a way of measuring astronomical distances in space . That doesn't make much sense because "light-year" contains the word "year," which is normally a unit of time . Even so, light-years measure distance.

Here on Earth we are used to measuring all distances in either inches/feet/miles or centimeters/meters/kilometers, depending on where you live and what method of measurement is used. Thanks to school, most people know how long a foot or a meter is — we are comfortable with these units because we use them every day. Light-years, not so much. Same thing with miles and kilometers — these are nice, human increments of distance that our minds can easily understand. Light-years, not so much.

Distances Light Travels in Space Are Gigantic

Who coined the term 'light-year', how far is one light-year.

When astronomers use their telescopes to look at stars , it's different. The distances in the universe are gigantic — or even within our Milky Way galaxy . For example, the closest star to Earth (besides our sun ) is called Proxima Centauri , and it is something like 24,000,000,000,000 miles (38,000,000,000,000 kilometers) away. That's the closest star, and there are so many zeros that most people aren't sure which -illion suffix to use (it's 24 trillion miles, or 38 trillion kliometers).

There are stars that are billions of times farther away than that. When you start talking about those kinds of distances, a mile or kilometer just isn't a practical unit to use because the numbers get too big, even when you step up to billions and trillions of them. No one wants to write or talk about numbers that have 20 digits in them! That's where light-years come in.

To measure really long distances and how fast light travels, astronomers and other scientists use a unit called a light-year. To reach the previously mentioned Proxima Centauri, it'd take 4.25 years at light speed.

The term "light-year" was first coined by German scientist, astronomer, mathematician and physicist Friedrich Bessel in 1838, when he measured the distance from Earth to a star called 61 Cygni, and came up with a distance of 660,000 times Earth's orbital radius.

He calculated that light would take about 10 years to get to 61 Cygni from Earth. Later, astronomers adopted the term and "light-years" quickly became standard to help make sense of the massive distances between basically everything in our vast universe.

So what exactly are light-years — or rather, how far is one light-year? Light travels at 186,000 miles per second (300,000 kilometers per second). Therefore, a light second is 186,000 miles (300,000 kilometers). A light-year is the distance that light travels in a year, or:

186,000 miles/second * 60 seconds/minute * 60 minutes/hour * 24 hours/day * 365 days/year = 5,865,696,000,000 miles/year

One light-year is 5,865,696,000,000 miles (9,460,800,000,000 kilometers). Light-years are a long way!

Using a light-year as a distance measurement has another advantage — it helps you determine age. Let's say that a star is 1 million light-years away. The light from that star has traveled at the speed of light to reach our planet. Therefore, it has taken the star's light 1 million years to get to our planet, and the light we are seeing was created 1 million years ago. So the star we are seeing is really how the star looked a million years ago, not how it looks at this moment from our viewpoint.

In the same way, our sun is 8 or so light minutes away. If the sun were to suddenly explode right now, we wouldn't know about it for eight minutes because that is how long it would take for the light of the explosion to get to Earth.

A light nanosecond — the distance light travels in a billionth of a second — is about 1 foot (about 30 centimeters). Radar uses this fact to measure how far away something like an airplane is. A radar antenna sends out a short radio pulse and then waits for it to echo off an airplane or other similar target. While it's waiting, it counts the number of nanoseconds that pass. Radio waves travel at the speed of light, so the number of nanoseconds divided by two tells the radar unit how far away the object is.

Light-year FAQ

What is a light-year in simple terms, is a light-year 365 days, how many light-years away is the sun from earth, lots more information, related articles.

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light travel in a year

Unraveling the Mysteries of Light-years: How Far Does Light Travel in a Year?

Unraveling the Mysteries of Light-years: How Far Does Light Travel in a Year?

Table of Contents

Introduction

The universe has always been a source of wonder and curiosity for humanity. One of the most intriguing concepts in the field of astronomy is the “light-year.” But what exactly is a light-year? How does it relate to our everyday understanding of distance , and what profound insights does it offer into the vastness of the cosmos? In this comprehensive exploration, we will delve deep into the world of light-years, shedding light on this captivating astronomical unit of measurement.

The Basics of Light-years

What is a Light-year?

A light-year, often abbreviated as “ly,” is a fundamental unit of measurement in astronomy. Contrary to what the name might suggest, it has nothing to do with time; rather, it quantifies distance on an astronomical scale. Specifically, a light-year represents the distance that light travels in the span of one Earth year through the vacuum of space.

The Speed of Light

Before we can fully grasp the significance of a light-year, we must first understand the incredible speed of light. In a vacuum, such as outer space, light travels at an astonishing speed of approximately 299,792,458 meters per second (about 186,282 miles per second). This cosmic speed limit is the fastest anything can move in the universe, and it plays a central role in the definition of a light-year.

Crunching the Numbers: How Far is a Light-year?

Measuring Distances in Space

To appreciate the enormity of a light-year, we need to consider the vastness of space. Traditional units of measurement, like meters or kilometers, are inadequate for expressing the vast distances between celestial objects. This is where light-years come into play, providing a more practical and comprehensible scale for measuring these cosmic spans.

So, just how far is a light-year in more familiar units? To put it in perspective, one light-year is approximately equal to 9.461 trillion kilometers (about 5.878 trillion miles). This mind-boggling distance dwarfs any terrestrial measurements we encounter in our daily lives.

Exploring Proxima Centauri: Our Closest Neighbor

As an example of the practicality of light-years in astronomy, let’s consider our nearest stellar neighbor, Proxima Centauri. This red dwarf star, part of the Alpha Centauri star system, is located a mere 4.22 light-years away from Earth. While 4.22 light-years might sound relatively close in astronomical terms, the actual distance is an astronomical 39.9 trillion kilometers (approximately 24.8 trillion miles).

Applications of Light-years in Astronomy

Studying Distant Stars and Galaxies

The concept of light-years is indispensable in the field of astronomy, especially when dealing with objects situated far beyond our solar system. When we look at stars or galaxies in the night sky, we are observing them as they were when their light set out on its journey toward Earth. This means that the light we see from these objects today may have been traveling through space for thousands, millions, or even billions of years.

Determining Age and Distance

Light-years also play a pivotal role in determining the age and distance of celestial objects. Astronomers use the time it takes for light to reach us from these objects to calculate their distance from Earth. This technique , known as “stellar parallax,” involves measuring the apparent shift in a star’s position when viewed from different vantage points in Earth’s orbit. By knowing the angle of this shift and the distance between those vantage points, scientists can accurately determine the distance to the star in question.

The Hubble Ultra-Deep Field: Peering Back in Time

A prime example of the power of light-years in astronomy is the Hubble Ultra-Deep Field (HUDF) image. Captured by the Hubble Space Telescope , this image showcases a tiny patch of sky that appears utterly dark to the naked eye. However, the HUDF reveals thousands of galaxies, each containing billions of stars, all located billions of light-years away from Earth.

This extraordinary image allows astronomers to glimpse the universe’s past, as the light from these galaxies has been traveling toward us for billions of years. Essentially, the Hubble Ultra-Deep Field offers a snapshot of the cosmos as it appeared billions of years ago, shedding light on the universe’s evolution over vast stretches of time.

The Limitations of Light-years

Time Travel and the Speed of Light

While light-years are an invaluable tool for astronomers, they also highlight one of the universe’s most intriguing constraints: the finite speed of light. As we observe objects situated light-years away, we are effectively peering into the past. The light we see left those objects long before the present moment, allowing us to witness celestial events that occurred in the distant past.

For example, if we were to observe a star located 1,000 light-years away, we would be seeing that star as it existed 1,000 years ago. This temporal discrepancy raises fascinating questions about time travel, the nature of causality, and our ability to study the universe’s history through the observation of distant objects.

The Observable Universe

Another limitation of light-years is that they define the boundary of what we can observe, known as the “observable universe.” Since the universe is roughly 13.8 billion years old (as of the latest measurements), the farthest objects we can observe are approximately 13.8 billion light-years away.

This concept might seem contradictory at first glance. If the universe is 13.8 billion years old, how can we see objects that are 13.8 billion light-years away? The answer lies in the expansion of the universe. Over cosmic time, the universe has been expanding, causing galaxies to move away from each other. The light from distant objects has had time to reach us because, during its journey, the universe itself has expanded, effectively lengthening the distance that light can travel in the same amount of time.

The Cosmic Implications of Light-years

Exploring Exoplanets

Light-years are not only crucial for studying stars and galaxies but also for investigating exoplanets—planets that orbit stars beyond our solar system. When astronomers discover an exoplanet , they often report its distance from Earth in terms of light-years. This information is vital for assessing the planet’s potential habitability and its relationship to its host star.

The Search for Extraterrestrial Intelligence (SETI)

The Search for Extraterrestrial Intelligence, or SETI, is an ongoing scientific effort to detect signals or signs of intelligent life beyond Earth. When researchers scan the cosmos for potential signals, they take into account the vast distances involved and the time it takes for signals to travel through space. This means that any signals we receive from extraterrestrial civilizations could be thousands or even millions of years old by the time they reach us.

Interstellar Travel and the Challenge of Distance

Light-years also pose significant challenges for the concept of interstellar travel. While science fiction often depicts humans traveling to distant stars and planets , the reality of such journeys is far more daunting. The nearest stars, even at just a few light-years away, present immense logistical and technological challenges for interstellar exploration. The immense distances involved mean that travel at or near the speed of light, if achievable, would still take centuries or even millennia to reach even the closest stars .

Proposed concepts for interstellar travel include advanced propulsion systems, such as theoretical “warp drives” or “wormholes.” However, these ideas remain in the realm of scientific speculation and face numerous theoretical and practical obstacles.

Cosmic Evolution and the Age of the Universe

The concept of light-years also plays a crucial role in our understanding of the universe’s age and evolution. By observing objects at various distances from Earth, astronomers can piece together a timeline of cosmic events. This timeline includes the formation of stars, galaxies, and the universe itself.

For instance, when astronomers observe distant galaxies billions of light-years away, they are essentially observing galaxies as they existed billions of years ago. This enables them to study the early stages of galaxy formation and evolution, shedding light on the universe’s transformation over vast stretches of time.

Cosmic Mysteries and Dark Matter

Light-years are central to unraveling some of the universe’s greatest mysteries, such as dark matter. Dark matter is a mysterious, invisible substance that makes up a significant portion of the universe’s mass, yet it does not emit, absorb, or interact with light. As a result, it cannot be directly observed. Instead, astronomers infer its presence through its gravitational effects on visible matter.

One way scientists study dark matter is by observing its gravitational influence on galaxies and galaxy clusters. The light from distant galaxies, affected by the gravitational pull of dark matter, exhibits characteristics that allow astronomers to deduce the presence of this enigmatic substance.

Cosmic Expansion and Dark Energy

The concept of light-years also ties into the cosmic phenomenon of dark energy. Dark energy is an even more mysterious component of the universe that seems to be responsible for the observed accelerated expansion of the cosmos. The presence of dark energy, inferred through measurements of cosmic expansion, adds another layer of complexity to the universe’s behavior.

As we observe distant galaxies and measure their redshift due to cosmic expansion, we gain insights into the prevalence and influence of dark energy. These observations provide critical data for cosmologists seeking to understand the fundamental forces governing the universe’s fate.

The Human Perspective

Human Exploration and Light-years

While light-years are primarily a tool of astronomers and astrophysicists, they also capture the human imagination. The vastness of the universe, as measured in light-years, inspires a sense of wonder and curiosity that has driven human exploration for centuries.

For example, consider the concept of “generation ships.” These hypothetical spacecraft would be designed for long-duration interstellar journeys, with the understanding that the generations aboard would live and die on the vessel before reaching their destination. The vast distances involved, expressed in light-years, prompt questions about the resilience and adaptability of future spacefaring generations.

Science Fiction and Light-years

Science fiction literature and films often feature light-years prominently in their storytelling. From the warp drives of “Star Trek” to the hyperdrives of “Star Wars,” these fictional technologies enable characters to traverse immense cosmic distances in the blink of an eye. While these concepts are currently speculative, they reflect our enduring fascination with the idea of exploring distant stars and galaxies.

The Pale Blue Dot

Perhaps one of the most iconic images that encapsulates our perspective on the universe is the “Pale Blue Dot.” This photograph, taken by the Voyager 1 spacecraft in 1990, shows Earth as a tiny, pale blue speck in the vastness of space. The image was taken from a distance of about 6 billion kilometers (nearly 4 billion miles) away from Earth, emphasizing the cosmic scale of our home planet .

In the context of light-years, the Pale Blue Dot serves as a poignant reminder of our place in the universe. It underscores the minuscule size of our world relative to the distances that light can travel in a single year.

Advanced Concepts and Future Discoveries

Time Dilation and Relativity

As our understanding of the universe continues to evolve, so too does our grasp of the intricate relationship between light-years, time, and space. Albert Einstein’s theory of relativity, which includes both special and general relativity , has profound implications for the measurement of time and space in the cosmos.

One of the consequences of Einstein’s theories is time dilation, which occurs when an object travels at a significant fraction of the speed of light. According to special relativity, time slows down for a moving object relative to a stationary observer. This means that as we approach the speed of light, time appears to pass more slowly for the traveler.

Time dilation has practical implications for space travel, particularly for journeys covering vast distances. While it might take thousands of years in Earth’s reference frame to reach a distant star at sublight speeds, time dilation could make the journey more manageable for the travelers on board the spacecraft. This fascinating aspect of relativity challenges our intuitive understanding of time and adds complexity to the concept of light-years in interstellar travel.

Quantum Entanglement and Faster-Than-Light Communication?

In the realm of quantum physics, another intriguing concept emerges that challenges our understanding of light-years and communication. Quantum entanglement, a phenomenon where particles become linked in such a way that the state of one particle instantaneously influences the state of the other, has been the subject of much scientific investigation and debate.

Some theorists have proposed that quantum entanglement could be used to transmit information instantaneously over vast distances, potentially rendering the constraints of light-years obsolete for communication. However, these ideas remain highly speculative and face significant practical challenges, including the preservation of entanglement over long distances.

The Search for Exotic Physics

In the quest to unravel the mysteries of the universe, scientists are continually pushing the boundaries of our understanding. The study of exotic physics, such as wormholes and warp drives, continues to captivate the imagination of both researchers and the public.

Wormholes, often featured in science fiction, are hypothetical passages through space-time that could potentially connect distant parts of the universe. If they exist, they could offer a means of traveling vast distances in a shorter amount of time, effectively bypassing the constraints of light-years. However, the existence of wormholes remains purely theoretical, and their practicality is uncertain.

Similarly, warp drives, inspired by the works of physicist Miguel Alcubierre, propose a method of propulsion that would contract space in front of a spacecraft while expanding it behind, allowing for faster-than-light travel. While these concepts are fascinating, they rely on speculative physics and face numerous obstacles, including the requirement for exotic forms of matter with negative energy.

The Ongoing Journey of Exploration

A Window into the Cosmos

The concept of light-years serves as a window into the vast, intricate, and awe-inspiring cosmos that surrounds us. It reminds us that when we gaze at the stars in the night sky, we are not just seeing the present; we are witnessing the distant past. Each point of light, each celestial body, carries with it a story of its own, a tale of cosmic evolution unfolding over billions of years.

Light-years challenge our comprehension and inspire us to continue exploring the mysteries of the universe. They beckon us to push the boundaries of human knowledge, to develop new technologies, and to reach for the stars in our quest for understanding.

As we stand on the precipice of the unknown, armed with the knowledge and tools to measure the inconceivable distances of the cosmos, we are reminded that the universe is a vast tapestry of light and time, waiting to be explored and unraveled by future generations of astronomers, scientists, and explorers.

The concept of light-years has illuminated the darkest corners of the universe, allowing us to glimpse the past, study the present, and imagine the future. It has given us the ability to measure and understand the incomprehensible distances between celestial objects and has inspired us to continue our journey of exploration and discovery.

From the study of distant galaxies to the search for extraterrestrial life , from the mysteries of dark matter to the possibilities of interstellar travel, light-years remain an essential tool in our quest to understand the cosmos. They challenge our perceptions of time and space, inviting us to explore the furthest reaches of the universe and expand the boundaries of human knowledge.

As we look to the stars and ponder the mysteries of the universe, let us remember that the concept of light-years is not just a measurement of distance; it is a measure of our curiosity, our ingenuity, and our unquenchable thirst for knowledge. It is a reminder that the universe is vast and wondrous, and that there is still so much left to discover, waiting to be illuminated by the light of human understanding.

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Light Year Conversion

What is light year, how to convert light years to miles, how to convert light years to kilometers, how to convert light years to astronomical units.

With this light year conversion tool, we aim to help you convert light year into different length units . To understand more on this topic, please check out our speed of light calculator and light year calculator .

We have written this article to help you understand the following:

  • What light year is ;
  • How to convert light years to miles ;
  • How to convert light years to kilometers ; and
  • How to convert light years to meters .

We will also demonstrate some examples to help you understand the light year conversion calculation.

A light year is the distance that light travels in one year, which is about 5.88 trillion miles or 9.46 trillion kilometers . Because the speed of light is constant, this distance provides a useful way to measure the vast distances in space.

For example, the closest star to Earth, Proxima Centauri, is about 4.24 light years away, meaning that the light we see from that star today left it over four years ago.

To convert light years into miles or kilometers, we need to multiply the distance in light years by the number of miles or kilometers in one light year, which is 5.88 trillion miles (9.46 trillion km) .

For example, if we want to know how many miles are in 3 light years, we would multiply 3 by 5.88 trillion miles to get 17.64 trillion miles.

For the conversion of light years into kilometers, we need to multiply the distance in light years by the number of miles or kilometers in one light year . One light year is approximately 9.46 trillion kilometers , so we can use this conversion factor to convert between the two units.

For example, if we want to know how many kilometers are in 2 light years, we would multiply 2 by 9.46 trillion kilometers to get 18.92 trillion kilometers.

Another unit of measurement often used in astronomy is the astronomical unit (AU) , which is the average distance between the Earth and the Sun . This distance is approximately 93 million miles (150 million kilometers) and is often used to measure distances within our own solar system.

For the conversion of light years into astronomical units, we need to divide the distance in light years by the number of light years in one astronomical unit, which is 0.000015813 .

For example, if we want to know how many astronomical units are in 5 light years, we would divide 5 by 0.000015813 to get approximately 316,602 astronomical units.

With our calculator, we can also help you convert light years into Earth radii, Sun radii, and megaparsecs. You can also check out our length converter to understand more about this topic.

It's worth noting that these distances are so vast that they are difficult to comprehend. Even the distance to our closest star, Proxima Centauri, is so large that it would take over 30,000 years to travel there at the speed of our fastest spacecraft.

What is 1 light year converted to miles?

1 light year is approximately 5.88 trillion miles . 1 light year is converted to miles by multiplying 1 by 5.88 trillion.

Is a light year a unit of time or distance?

A light year is a unit of distance , specifically the distance that light travels in one year.

Can we travel faster than the speed of light?

According to our current understanding of physics, it is not possible for anything with mass to travel faster than the speed of light .

How to convert light years to meters?

You can convert light years into meters in 3 steps:

  • Determine the number of light years to convert.
  • Multiply the number of light years by 9,461 trillion.
  • Analyse the results in meters.

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When is daylight saving time 2024? Millions have sunsets after 6 pm as time change approaches

light travel in a year

Do you feel it in the air? Spring is coming, and the start of longer daylight hours is well underway.

And with daylight saving time starting in March, most Americans will soon have even more hours in the sun. Even ahead of of the time change, there are already cities in every continental U.S. time zone that are reporting sunset times after 6 p.m. as the Earth and the Northern Hemisphere begins its tilt toward the sun.

The time adjustment affects the daily lives of hundreds of millions of Americans, prompting clock changes, contributing to  less sleep  in the days following and, of course, later sunsets.

Here's what to know about the start of daylight saving time in 2024.

When is daylight saving time in 2024?

Daylight saving time will begin for 2024 on Sunday, March 10 at 2 a.m. local time, when our clocks will go ahead one hour, part of the twice-annual time change that affects millions, but not all , Americans.

Have the days been getting longer?

The winter solstice, which occurs annually on Dec. 21, is the day with the shortest daylight hours each year. Since then, the days have been gradually getting longer.

Because the sun rises in the east and sets in the west , cities that are located eastward experience sunrise before more more westward cities.

Ahead of daylight saving time, which starts this month, some areas are already experiencing later sunset times. On the East Coast, parts of states like Maine , New Hampshire , Vermont , New York and Connecticut are already recording sunsets after 5:30 p.m. ET, according to TimeandDate.com .

Sunset times get later as you move westward though time zones, and cities on the western edge of Eastern Standard Time like Detroit and Indianapolis have sunsets around 6:30 p.m. ET.

The same concept plays out in each of the continental United States' four time zones, with cities on the easternmost edge of each time zone recording sunset times roughly between 5:30 and 5:45 p.m. local time.

What is daylight saving time?

Daylight saving time  is the time between March and November when most Americans adjust their clocks by one hour.

We lose an hour in March (as opposed to gaining an hour in the fall) to accommodate for more daylight in the summer evenings. When we "fall back" in November, it's to add more daylight in the mornings. 

When is the spring equinox?

In the Northern Hemisphere, the vernal, or spring equinox is March 19, marking the start of the spring season. 

When does daylight saving time end in 2024?

In 2024, daylight saving time will end for the year at 2 a.m. local time on Sunday, Nov. 3. It will pick up again next year on Sunday, March 9, 2025.

Is daylight saving time ending permanently?

The push to stop changing clocks was put before Congress in the last couple of years, when the U.S. Senate unanimously approved the  Sunshine Protection Act  in 2022, a bill that would make daylight saving time permanent. However, it did not pass in the  U.S. House of Representatives  and, therefore, was not signed into law by President Joe Biden.

A  2023 version of the act  remained idle in Congress as well.

Does every state observe daylight saving time?

Not all states and U.S. territories  participate  in daylight saving time.

Hawaii and Arizona (with the exception of the Navajo Nation) do not observe daylight saving time, and neither do the territories of American Samoa, Guam, the Northern Mariana Islands, Puerto Rico and the U.S. Virgin Islands.

Because of its desert climate,  Arizona  doesn't follow daylight saving time. After most of the U.S. adopted the Uniform Time Act, the state figured that there wasn't a good reason to adjust clocks to make sunset occur an hour later during the hottest months of the year.

The Navajo Nation, which spans Arizona, Utah and New Mexico, does follow daylight saving time.

Hawaii is the other state that does not observe daylight saving time. Because of its proximity to the equator, there is not a lot of variance between hours of daylight during the year.

Sailor Cole Brauer makes history as the first American woman to race solo around the world

Aboard her 40-foot racing boat First Light ,  29-year-old Cole Brauer just became the first American woman to race nonstop around the world by herself.

The New York native pulled into A Coruña, Spain, on Thursday after a treacherous 30,000-mile journey that took 130 days.

She thanked a cheering crowd of family and fans who had been waiting for her on shore.

“This is really cool and so overwhelming in every sense of the word,” she exclaimed, before drinking Champagne from her trophy.

The 5-foot-2 powerhouse placed second out of 16 avid sailors who competed in the Global Solo Challenge, a circumnavigation race that started in A Coruña with participants from 10 countries. The first-of-its-kind event   allowed a wide range of boats to set off in successive departures based on performance characteristics. Brauer started on Oct. 29, sailing down the west coast of Africa, over to Australia, and around the tip of South America before returning to Spain.

Brauer is the only woman and the youngest competitor in the event — something she hopes young girls in and out of the sport can draw inspiration from.

“It would be amazing if there was just one girl that saw me and said, ‘Oh, I can do that too,’” Brauer said of her history-making sail.

It’s a grueling race, and more than half of the competitors have dropped out so far. One struck something that caused his boat to flood, and another sailor had to abandon his ship after a mast broke as a severe storm was moving in.

The four-month journey is fraught with danger, including navigating the three “Great Capes” of Africa, Australia and South America. Rounding South America’s Cape Horn, where the Atlantic and Pacific Oceans meet, is often likened to climbing Mount Everest because of its perfect storm of hazards — a sharp rise in the ocean floor and whipping westerly winds push up massive waves. Combined with the frigid waters and stray icebergs, the area is known as a graveyard for ships, according to NASA. Brauer  said  she was “so unbelievably stoked” when she sailed past Cape Horn in January.

Marco Nannini, organizer of the Global Solo Challenge, said the comparison to scaling Mount Everest doesn’t capture the difficulty of the race. Sailing solo means not just being a skipper but a project manager — steering the boat, fixing equipment, understanding the weather and maintaining one’s physical health.

Nannini cited the relatively minuscule number of people who have sailed around the world solo — 186, according to the International Association of Cape Horners — as evidence of the challenges that competitors face. More than 6,000 people have climbed Mount Everest, according to  High Adventure Expeditions .

Brauer stared down 30-foot waves that had enough force to throw her across the boat. In a scare caught on camera, she badly injured her rib   near the halfway point of the event. At another point, her team in the U.S. directed Brauer to insert an IV into her own arm due to dehydration from vomiting and diarrhea.

She was able to stay in constant communication with members of her team, most of whom are based in New England,   and keep herself entertained with Netflix and video calls with family through Starlink satellites.   That’s also how Brauer was able to use Zoom to connect with NBC News for an interview, while she was sailing about 1,000 miles west of the Canary Islands.

While Brauer was technically alone on First Light, she had the company of 450,000 followers on Instagram, where she frequently got candid about life on an unforgiving sea while reflecting on her journey.

“It all makes it worth it when you come out here, you sit on the bow, and you see how beautiful it is,” she said in an Instagram video, before panning the camera to reveal the radiant sunrise.

Brauer grew up on Long Island but didn’t learn to sail until she went to college in Hawaii. She traded in her goal of becoming a doctor for life on the water. But she quickly learned making a career as a sailor is extremely difficult, with professional racers often hesitant to welcome a 100-pound young woman on their team.

Even when she was trying to find sponsors for the Global Solo Challenge, she said a lot of people “wouldn’t touch her with a 10-foot pole” because they saw her as a “liability.”

Brauer’s message to the skeptics and naysayers? “Watch me.”

“I push so much harder when someone’s like, ‘No, you can’t do that,’ or ‘You’re too small,’” Brauer explained.

“The biggest asset is your mental strength, not the physical one,” Nannini said. “Cole is showing everyone that.”

Brauer hopes to continue competing professionally and is already eyeing another around-the-world competition, but not before she gets her hands on a croissant and cappuccino.

“My mouth is watering just thinking about that.”

Emilie Ikeda is an NBC News correspondent.

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A hot air balloon over Melbourne skyline

Chinese tourism to Australia still in the doldrums after pandemic travel bans

Tourism industry disappointed but hopeful Chinese holidaymakers could return by year’s end – but economists predict a longer wait

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In the two weeks either side of lunar new year, Mandy Ho, who manages a hot air balloon company in Melbourne, has many balls in the air.

Most mornings before dawn, when weather permits, her colleagues fly Chinese tourists from the vineyards of the Yarra Valley over Melbourne’s eastern suburbs to parkland on the city’s fringe. Interpreters make sure nothing is lost in translation.

Ho has spent weeks preparing tourists and arranging buses to collect them from hotels. She’s already met some of them while running the company’s Mandarin smartphone app, website and Chinese social media channels.

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But this year, she’s noticed a shift. Ho says Chinese tourist numbers are still down by about half when compared with pre-pandemic levels. It’s a financial hit for the company, Global Ballooning, as the Chinese market brings in about 50% of its clients.

“I was expecting a full recovery this year as it’s the first year they can travel overseas for Chinese new year,” Ho says. “But it’s been a much slower recovery than what we expected.”

A hot air balloon prepares to take off in Melbourne. The Chinese market accounts for about 50% of the clients of one Melbourne company.

Ho isn’t the only tourism operator disappointed by the sluggish return of Chinese tourists. Tourism Australia figures show 102,000 Chinese holidaymakers visited Australia in September 2023. Four years earlier, the number was 688,000 in the same month.

“I think there’s a few reasons for this,” Ho says.

“The economy in China isn’t great and a lot of people are choosing to go to Singapore, Thailand and Malaysia because they’re visa-free. This is the first year they’ve been able to travel since the pandemic and they’re preferring short-haul flights.”

Ho’s analysis is supported by statistics from booking platform Trip.com, which has reported a 30% increase in Chinese tourism to south-east Asia in recent weeks, compared with 2019 levels. Trips to Hong Jong, Japan and South Korea have also increased.

As Chinese tourists take their money elsewhere, Ho and other tourism providers have had to get creative.

“We tried not to put all our eggs in the one basket,” Ho says. “We diversified our market and this year we’re seeing a lot people coming back from the United States, from Taiwan and Hong Kong, too.”

‘We’re not hitting alarm bells just yet’

Peter Shelley from the Australian Tourism Export Council, a peak body for tourism operators, says many of his members are also disappointed but are not panicking.

“If we are honest, I think we were all hoping it would be a little bit more buoyant. It was never going to be 100%, we hoped it would be about 75%,” Shelley says.

“Are we worried about it? I don’t think anyone is hitting the alarm bells just yet. It’s still early days, and maybe by the end of the year we’ll be back to 2019 levels.”

Shelley says many Chinese consumers now realise Australia is an expensive country to visit and fly to. This month, there’s about 170 scheduled flights between China and Australia. That’s 86% of all flights during the same month in 2019.

Tourism Australia, a government agency that promotes holiday making, knows what’s at stake. In 2019, Chinese visitors spent $12.4m in Australia. The agency hopes tourism will return to pre-pandemic levels by the end of the year, despite Oxford Economics suggesting that may not happen until 2025-26.

“[While] travel with China reopened a year later than other markets, we are confident about its recovery as the market continues to steadily rebuild,” a Tourism Australia spokesperson says.

Airline passengers make their way through Melbourne Airport in Melbourne

But some experts are concerned by anecdotal evidence this past fortnight. Dr Paul Stolk, a senior lecturer in tourism at Newcastle University, says this lunar new year was a litmus test on the health of the Chinese market.

“This is the period of time where we should see a lot of activity,” Stolk says. “This period we are in right now could be really telling in terms of whether we will see any bounce back and where it will occur, including capital cities and regional hotspots.”

‘We’ve been back to normal’

The Great Ocean Road – a long winding roadway that hugs the south-eastern Victorian coastline over steep cliffs – is usually filled with busloads of Chinese tourists. For years, signs by the side of the road have reminded Chinese tourists to drive in the left lane.

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Before the pandemic, some restaurants in coastal towns along this road printed menus in Mandarin. After years of lockdowns, many business owners hoped the Chinese tourists would rush back to the coastline and help them rebound.

A coastal section of the Great Ocean Road, just outside Lorne. Chinese tourist numbers along the stretch have failed to recover post-pandemic.

Liz Price, the general manager of Great Ocean Road Regional Tourism, acknowledges the Chinese tourism market has been slow to recover in the region. But she says recent weeks give some cause for optimism.

“We have had some reports that the numbers have increased over the summer and there has been some growth in coaches day-tripping out of Melbourne,” Price says.

This may be due to the Australian government reissuing group visas for Chinese travellers in September. Dr Maneka Jayasinghe, a tourism expert at Charles Darwin University, says this should lead to an increase in tourists in coming months.

Sally Cannon, who runs the Apollo Bay Bakery about two-and-a-half hours drive west of Melbourne, which claims to be the home of the scallop pie on the Great Ocean Road, is also optimistic.

Unlike Ho, Cannon has noticed an increase in Chinese tourists over the last two weeks. So, too, have other business owners closer to Melbourne, in Lorne. Cannon says she’s hopeful the numbers will continue to rise.

“Pre-Covid, Chinese tourists were a big part of our business,” Cannon says. “Over the past few years, we’ve managed to continue without them, but it’s nice to see them return.

“This has been the first year since Covid where it’s felt we’ve been back to normal. I just have this feeling it will continue.”

‘It was like a green light’

Like many sections of the Australian economy, political tensions between Beijing and Canberra have had some impact on tourism. But analysts differ on the how significant the influence has been.

Tom Parker, the chief executive of the Australia China Business Council, says tensions may have played a role in tourism numbers until prime minister Anthony Albanese’s trip to Beijing in November – the first by an Australian leader in seven years.

“Symbolism is important in China,” Parker says.

“This trip certainly symbolised a lot within China, including that it was OK to engage with Australia again. It was like a green light. These things are never said directly, but the visit, at that leadership level, told a story.”

Shelley says the impact of geopolitical tensions would have been clearer if the borders had been open during the pandemic era.

“If we were talking about this a few years ago, I think the impact would have been quite high,” Shelley says. “I must say, the current government has smoothed the waters but there could still be an undertone of tension.”

Ho believes the enduring appeal of the Australian landscape will always attract tourists from China, no matter the political climate. She just hopes they won’t wait too long to return.

“I definitely think they will come back,” Ho says. “There’s just so much to offer. By the end of this year, I’m sure the numbers will have increased.”

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March Is the Best Time of Year to See the Northern Lights—Here's Why

Even better: 2024 is expected to bring the strongest auroral activity we've seen in 20 years.

light travel in a year

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If seeing the northern lights is on your bucket list, this month is a great time to turn that dream into reality. According to SpaceWeather.com , March is the best time of year on record for viewing the aurora borealis.

Auroras are ribbons of light that weave across earth's northern or southern polar regions. These natural light shows are caused by magnetic storms that are triggered by solar activity. When these particles enter earth's magnetosphere, they cause substorms, which then slam into our atmosphere and collide with earth's oxygen and nitrogen particles. As these air particles shed the energy they picked up from the collision, each atom starts to glow in a different color.

During March, this phenomenon occurs more than it does in other months, according to a 75-year-long study by retired NASA solar physicist David Hathaway. The study shows that March has more geomagnetically active days than any other month of the year.

In fact, geomagnetic disturbances are almost twice as likely to occur in spring and fall vs. winter and summer. SpaceWeather.com reports that this is due to the fact that cracks tend to form in Earth's magnetosphere during weeks around equinoxes, allowing solar wind to create Northern Lights. This year, the Spring equinox occurs on March 19.

In general, 2024 is expected to be a big year for viewing the Northern Lights due to increased solar activity. Scientists even believe that this year will bring the strongest auroral activity we've seen in 20 years.

While the Northern Lights have historically made an appearance in the most northern parts of the northern hemisphere, like Alaska, Norway, and Sweden, there have been recent sightings in various parts of the country, including Minnesota, Pennsylvania, and Ohio.

Space Technology 5. NASA National Aeronautics and Space Administration .

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Enter the Year of the Dragon: A 2024 guide to Lunar New Year

At this very moment, millions of people around the world are busy preparing for one of the year’s biggest festivals – Lunar New Year, which marks the first new moon of the lunar calendar.

This year, it falls on February 10, kicking off the 15-day Spring Festival.

Whether you’re unfamiliar with Lunar New Year or need a refresher, this guide will highlight some of the most common traditions associated with the occasion.

Why is it the Year of the Dragon?

Though incredibly complex, the Chinese zodiac calendar is best described as a 12-year cycle represented by 12 different animals, in this order: Rat, Ox, Tiger, Rabbit, Dragon, Snake, Horse, Goat, Monkey, Rooster, Dog and Pig.

Your personal zodiac animal sign is determined by your year of birth, meaning 2024 will welcome plenty of baby dragons to the world. Those born in 2025 will be snakes, and so on.

Followers believe that for each Chinese zodiac sign, luck will depend largely on the positions of the Tai Sui – a collective name for the stellar deities thought to rotate parallel to and in the opposite direction of Jupiter.

Different geomancy masters may interpret the data differently, but there is usually a consensus on what the year means for each zodiac animal based on the positions of the stars.

Why light firecrackers and wear red? Meet Nian

There are countless folk tales attached to Lunar New Year, but the myth of “Nian” stands out as one of the most fun.

Legend has it Nian was a ferocious underwater beast with sharp teeth and horns. Every Lunar New Year’s Eve, it crawled onto the land and attacked a nearby village.

On one such occasion, as the villagers rushed into hiding, a mysterious old man showed up and insisted on sticking around despite being warned of impending doom.

To the villagers’ surprise, the old man and the village survived utterly unscathed.

The man claimed to have scared Nian away by hanging red banners on the door, lighting firecrackers and donning red clothing.

This is why wearing the fiery color, along with hanging red banners and lighting firecrackers or fireworks, are Lunar New Year traditions, all of which are still followed today.

The preparation

Fun aside, Lunar New Year can actually be a lot of work. Festivities often last for 15 days – sometimes even more – with different tasks and activities taking place over that period.

It all begins about a week ahead of the new year.

Festive cakes and puddings are made on the 24th day of the last lunar month (February 3 in 2024). Why? The word for cakes and puddings is “gao” in Mandarin and “gou” in Cantonese, which sound the same as the word for “tall.”

As a result, eating these treats is believed to lead to improvements and growth in the coming year. (If you haven’t prepared your own “gou” yet, here’s an  easy recipe for turnip cake , a beloved Lunar New Year dish.)

And don’t forget about our friend Nian. No Lunar New Year preparation would be complete without the aforementioned hanging of red banners bearing auspicious phrases and idioms (called fai chun in Cantonese, or chunlian, in Mandarin) at home – beginning with one’s front door.

These will perform double duty – keep Nian away and invite good fortune.

Not all prep work is fun. According to Lunar New Year tradition, a big cleanup should be carried out in homes on the 28th day of the last lunar month, which falls on February 7 this year.

The aim is to rid your home of any bad luck that’s accumulated over the past year.

And don’t clean anything again till February 12, or you’re washing away all that good luck that came in at the start of the new year.

On a related note, some say you shouldn’t wash or cut your hair on the first day of the new year either.

Why? The Chinese character for hair is the first character in the word for prosper. Therefore washing or cutting it off is seen as washing your fortune away.

You’ll also want to avoid purchasing footwear for the entire lunar month, as the term for shoes (haai) sounds like losing and sighing in Cantonese.

(Read more  Lunar New Year dos and don’ts here .)

Lunar New Year’s Eve: The big feast

A big family reunion dinner is usually held on Lunar New Year’s Eve, which falls on February 9 this year.

The menu is carefully chosen to include dishes associated with luck, including fish (the Chinese word for it also sounds like “surplus”), puddings (symbolizes advancement) and foods that look like gold ingots (like dumplings).

In China, the foods served at these classic dinners vary from north to south. For instance, northern Chinese tend to have dumplings and noodles, whereas southern Chinese can’t live without steamed rice.

But no matter which dishes you prefer, Lunar New Year foods are a feast of wordplay.

Lunar New Year’s Day: Family visits and red packets

The first few days of the Lunar New Year, especially the first two days, are often a test of one’s stamina, appetite and social skills, as many people have to travel and visit immediate family, other relatives and friends.

Bags are stocked with presents and fruits to give out at homes visited. Visitors will in turn be showered with gifts after exchanging conversations over Lunar New Year treats.

Married people also have to give out red packets to those who haven’t yet tied the knot – both children and unmarried juniors.

It’s believed these envelopes – known as hongbao/lai see – could protect children by warding off evil spirits called sui.

Day 3: Visit a temple

Day three of the Lunar New Year (which falls on February 12 in 2024) is named “chi kou/cek hau,” or red mouth.

It’s believed that arguments are more likely to happen on this day, so people will avoid social interactions and instead visit temples.

While there, some will use the opportunity to make offerings to offset any potential bad luck. As noted earlier, for many people  Lunar New Year is a time to consult the stars to find out what lies ahead in the coming months.

Every year, certain Chinese zodiac signs clash with the stars negatively so temple visits are considered a good way to resolve those conflicts and bring peace in the coming months.

Day 7: The people’s birthday

The seventh day of the Lunar New Year (February 16 in 2024) is said to be when the Chinese mother goddess, Nuwa, created humanity. Thus, it’s called renri/jan jat (the people’s birthday).

Different communities in Asia will serve various birthday foods on that day.

For instance, people in Malaysia enjoy yeesang, or a “Prosperity Toss” of raw fish and shredded vegetables, whereas Cantonese people eat sweet rice balls.

Day 15: The Lantern Festival

The highlight of the whole Spring Festival, the Lantern Festival happens on the 15th and final day (February 24 in 2024).

Called Yuan Xiao Jie in Mandarin Chinese, it’s considered the perfect ending to the weeks-long Lunar New Year preparations and celebrations.

The Lantern Festival celebrates the first full moon of the year – hence the name (Yuan means beginning. Xiao means night).

It marks the departure of winter and the beginning of the spring season.

On this day, people light lanterns to symbolize driving out darkness and bringing hope to the coming year.

In ancient Chinese society, it was the only day when young girls were allowed to go out to admire the lanterns and meet boys. As a result, it’s also been dubbed Chinese Valentine’s Day.

Nowadays, cities worldwide still put on massive lantern displays and fairs on the festival’s final day. Some Chinese cities, such as Chengdu, even host dramatic fire dragon dances .

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Tourists visit a Lunar New Year Lantern Festival in Shanghai on January 21, 2024. - Costfoto/Sipa USA

IMAGES

  1. How Far Does Light Travel in a Year?

    light travel in a year

  2. How Far Does Light Travel in a Year?

    light travel in a year

  3. How Much Light Travel In One Year

    light travel in a year

  4. Light year A unit of measure to indicate the distance that light travel

    light travel in a year

  5. What Is a Light-Year? :: NASA Space Place

    light travel in a year

  6. How Long To Travel A Light Year Calculator

    light travel in a year

COMMENTS

  1. How Far Does Light Travel in a 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...

  2. What Is a Light-Year?

    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?

  3. 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. Make the jump to light-years as we cruise through the Milky Way galaxy. Video credit: NASA/JPL-Caltech.

  4. How far is a light-year? Plus, distances in space

    So, a light-year is 5.88 trillion miles (9.46 trillion km). However, stars and nebulae - not to mention distant galaxies - are vastly farther than one light-year away. And, if we try to...

  5. Light-year

    A light-year, alternatively spelled light year ( ly ), is a unit of length used to express astronomical distances and is equal to exactly 9,460,730,472,580.8 km, which is approximately 5.88 trillion mi.

  6. How Far is a Light Year?

    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.

  7. Light-year

    Light-year, in astronomy, the distance traveled by light moving in a vacuum in the course of one year, at its accepted velocity of 299,792,458 metres per second (186,282 miles per second). A light-year equals about 9.46073 × 1012 km (5.87863 × 1012 miles), or 63,241 astronomical units. About 3.262

  8. What is a light year? Find out.

    February 20, 2013 A light-year is how astronomers measure distance in space. It's defined by how far a beam of light travels in one year - a distance of six trillion miles. Think of it as...

  9. What is a light-year?

    A light-year is a measure of astronomical distance: Light travels through a vacuum at precisely 983,571,056 feet (299,792,458 meters) per second, making a light-year approximately 6...

  10. What is a light-year?

    A light-year (ly) is the distance that light can travel in one year. In one year, light travels about 5,880,000,000,000 miles or 9,460,000,000,000 kilometers. So, this distance is 1 light-year. For example, the nearest star to us is about 4.3 light-years away.

  11. How fast does light travel?

    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...

  12. Cosmic Distances

    A light year is the distance a photon of light travels in one year, which is about 6 trillion miles (9 trillion kilometers, or 63,000 AU). Put another way, a light year is how far you'd travel in a year if you could travel at the speed of light, which is 186,000 miles (300,000 kilometers) per second.

  13. How Long Would It Take To Travel A Light Year

    How Long Would It Take To Travel A Light Year November 23, 2022 by David Ryan Using the fastest man-made vehicle, NASA's Juno spacecraft, which travels at 165,000 mph (365,000 kmph), it would take 2,958 years to travel a light year. A light year is equivalent to about 5.88 trillion miles (9.46 trillion kilometers).

  14. What is a light year? Why you might not be seeing stars in real time

    A light year is a measure of distance while mph (miles per hour) is a measure of speed. So, a light year cannot be measured in mph. Light travels at a constant speed of 670,616,629 mph which means ...

  15. Speed of light: How fast light travels, explained simply and clearly

    Observations of the cosmic microwave background, the light released when the universe was 380,000 years old, show that the speed of light hasn't measurably changed in over 13.8 billion years....

  16. What Is a Light-year?

    A light-year is the distance that light can travel in one year. Is a light-year 365 days? Yes, a light year is the distance traveled by light in a vacuum in one Julian year, which is equal to 365.25 days.

  17. Light Year Calculator

    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).

  18. Unraveling the Mysteries of Light-years: How Far Does Light Travel in a

    In a vacuum, such as outer space, light travels at an astonishing speed of approximately 299,792,458 meters per second (about 186,282 miles per second). This cosmic speed limit is the fastest anything can move in the universe, and it plays a central role in the definition of a light-year. Crunching the Numbers: How Far is a Light-year ...

  19. What is a light-year?

    Light travels at 299,792,458 meters (186,282.397 miles) per second. Multiply that number by the number of seconds in a year (31,557,600), and you get your answer: One ...

  20. What is a light year?

    A light year is the distance that light travels in a vacuum in one year. The speed of light is 300,000,000 meters/second, and there are 365 x 24 x 60 x 60 = 31,536,000 seconds in a year. Since distance = speed x time , that gives: 9.46 x 1015 meters = 1 light year, or. 9.46 x 1012 km,

  21. Light Year Conversion

    A light year is the distance that light travels in one year, which is about 5.88 trillion miles or 9.46 trillion kilometers.Because the speed of light is constant, this distance provides a useful way to measure the vast distances in space. For example, the closest star to Earth, Proxima Centauri, is about 4.24 light years away, meaning that the light we see from that star today left it over ...

  22. Convert Light Years

    A light year is the distance that light travels in one year. The year used by the International Astronomical Union is 365.25 days. A light year is defined as exactly 9,460,730,472,580.8 kilometers. Kilometers. A kilometer, or kilometre, is a unit of length equal to 1,000 meters, or about 0.621 miles. In most of the world, it is the most common ...

  23. Convert Light Years to Miles

    A light year is the distance that light travels in one year. The year used by the International Astronomical Union is 365.25 days. A light year is defined as exactly 9,460,730,472,580.8 kilometers. Miles A mile is a unit of distance equal to 5,280 feet or exactly 1.609344 kilometers.

  24. Daylight saving time 2024: Time change details; when to 'spring ahead'

    In 2024, daylight saving time will end for the year at 2 a.m. local time on Sunday, Nov. 3. It will pick up again next year on Sunday, March 9, 2025. Is daylight saving time ending permanently?

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    Aboard her 40-foot racing boat First Light, 29-year-old Cole Brauer just became the first American woman to race nonstop around the world by herself.

  26. What Is Daylight Saving Time, and When Does Time Change in 2024?

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    Tourism industry disappointed but hopeful Chinese holidaymakers could return by year's end - but economists predict a longer wait In the two weeks either side of lunar new year, Mandy Ho, who ...

  29. March Is the Best Time of Year to See the Northern Lights—Here's Why

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  30. Enter the Year of the Dragon: A 2024 guide to Lunar New Year

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