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# What is a Light Year

A light year is a measure of distance similar to a mile or a kilometer.
A light year is the distance that light can travel in a year.
One light-year is equal to 9,500,000,000,000 kilometers

So how far is that?

Light can travel around the earth 7 times in one second. That distance would be a light second since that is how far light can travel in a second. Since there are 60 seconds in a minute you multiply that distance by 60 and you have a light minute. That means light can circle the earth 420 times in one minute! Multiply by 60 to get a light hour. Multiply by 24 to get a light day (how far light can travel in a day). Multiply that by 365 and you get a light year which is the distance light can travel in a year.

The moon which is about 1.25 light seconds away from the earth. That is about the same distance as going 9 times around the earth. If you turned on a bright light on the moon it would take 1.25 seconds to reach the earth.

The distance light can travel in 60 seconds is a light minute. It takes light 8 minutes to travel from the sun to the earth, so the sun is 8 light minutes away. Another term for the distance from the earth to the sun is an Astronomical Unit (AU). That distance is like traveling around the earth 3360 times (7x60x8).

It takes light from the sun 340 minutes (5.7 hours) to travel from the sun to Pluto. That is equivalent to 39.5 AU. While that is only 5.7 light hours, if you travel at 100 km/hr it would take 60,000,000 hrs, which is 6849.3 years to reach pluto!

So now imagine how far light can travel in a year! At 100 km/hr it would take you 10,526,292 years to travel one light year!

Some Distances in Light Years
The star that is nearest to our sun is Proxima Centauri which is 4.2 light years away.
There are only eleven stars that are less then 10 light years away.
Our galaxy, the Milky Way, is about 100,000 light years across.
The closest galaxy to the Milky Way, Andromeda, is 2,500,000 light years away.
The most distant galaxy discovered is 12,800,000,000 light years away.
Who knows what is beyone that?

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