What is a light year?

The distance light travels (in a vacuum) in 1 year.

In a vacuum, light travels at 186,000 miles every second so in a minute it will tavel 60 times this amount (as there are 60 seconds in a minute).

In 1 hour (60 mins) it will travel 60 times this amount.

In 1 day (24 hrs) it will travel 24 times this amount.

In 1 year (365 days) it will travel 365 times this amount.

This amount is equivalent to around six million, million miles.

The nearest star (Proxima Centauri) is 4 1/4 light years away or approx. 25 million, million miles.

The galaxy is 100,000 light years across

The known universe is over 13 billion light years across.

If a star is 10,000 light years away, we are seeing it today as it was 10,000 years ago - as the light that started out then is only just reaching us. Similarly, if there we aliens looking at us through a powerful telescope on a planet that was just over 7 light years away, then they would just today, in 2008, be seeing 9/11 happening.

Answer

A Light Year is how far light travels in one year, about 10 trillion km.

Answer

A "light year" is the distance in which a particle of light will travel [in a year], through a pure vaccuum. It is useful in finding distances to very distant objects, and as we're assuming that there is a pure vaccuum between us and whatever you're looking at, we can then determine how long ago, in Earth years, that light originated from whatever we're looking at. It is entirely possible that some of the stars we can see from Earth are simply no longer there!

How far is it in more easily understandable terms? Well, the speed of light in a vaccuum is defined as something approximately 2.99 * 10^8 m / s. Figure out how many seconds in a year, then practice your algebraic skills to arrive at meters. Finally, convert meters to miles (if you're American) or kilometers (anywhere else). I'd do it, but I'm just too durn lazy.

Disclaimer: I am not an astronomer or physicist, but I'm nonetheless pretty certain of the above figures.

Answer

Light travels at a speed of 299,792,458 meters per second, or at approximately 186,282 miles per second, in a vacuum. A light year is defined as the distance a particle of light would travel in a year at this speed. There are 31,536,000 seconds in a 365 day year, so if you multiply that number by 186,282 miles, you will have the distance light would travel in a year. (approximately 5,874,589,152,000 miles) As noted above, a light year is used as a more convenient measure of astronomical distances.

It is easier to measure using the convenient metric system. A light year is approximately 9,454,254,955,000 kilometers long

First answer by JohnWelsh. Last edit by JohnWelsh. Contributor trust: 101 [recommend contributor]. Question popularity: 1 [recommend question]