What is a Lightyear?

Sometimes it may not make any sense to associate distance with a unit of time such as a year. LightyearThough that may be the case, a light year is not a measure of time. When we talk about light years we are talking about a measure of distance where units like miles, kilometers, meters, and other conventional units we are used to become quite insignificant. Understanding what is a light year will require knowing how astronomers measure large distances in empty space.

What is a Light Year?

In order to appreciate what is a light year, one must understand how far light travels given a specific amount of time. We know that light travels through a vacuum from the sun before it reaches planets and other members of our solar system. A light year refers to a distance that light can go over given a year’s length of travel.

Light can travel over 186,282 miles in one second. Now that is astoundingly fast, which translates to 299,792 kilometers if you want to use the metric system. Multiply that by the number of seconds you have in a year that will then total to a distance of 9.4 trillion kilometers or 5.8 trillion miles.

This is why such units of distance like miles and kilometers become insignificant when discussing travels in outer space. The distance that should be traveled across different heavenly bodies is just too great for the units we use conventionally here on earth.

Since astronomers have to discuss distances in such huge amounts they instead would use light years to describe them. Understanding this will give us a greater appreciation for what is a light year and how it helps us with a greater perspective.


Understanding what is a light year will give us an idea regarding its use and how more effective it is than our every day units of measure. For example, other than the sun, the closest star to our planet is around several trillion miles away or around 24,000,000,000,000 miles – give or take. Now that is only the next closest star to our planet. There are others that are really farther away than that one, which are actually billions of times further.

Other than describing great distances, light years are also used to determine the age of heavenly bodies that are seen through a telescope. For instance, a star is two million light years away from our planet. This simply means that the light we see in our telescopes here is what that star looked like two million years ago. It took that light two million years to get to us so that we may view it. What we see in our telescopes is actually not what distant objects look like today.

Appreciating its Use

Understanding what is a light year will help us appreciate how vast our universe is. Such units of distance that we are used to just won’t apply to objects that astronomers see using telescopes. It is used to measure distance and the age of objects in outer space.

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