A light year is a unit of

A. Time
B. Energy
C. Length
D. Mass
E. None of above

The correct answer is C) Length.

A light-year is a unit of length that is used to measure astronomical distances. It is the distance that light travels in one year in a vacuum. The speed of light is approximately 299,792,458 meters per second (about 186,282 miles per second) and it never changes. Therefore, a light-year is the distance that light travels in one year, which is about 9.461\times10^{12}kilometers (5.878\times10^{12}miles) or about 9.461 trillion kilometers (5.878 trillion miles). It is a very large unit of measurement, and it is often used to describe the distance between stars and galaxies.

For example, the nearest star to our solar system, Proxima Centauri, is about 4.22 light-years away. This means that the light we see from Proxima Centauri today left the star 4.22 years ago. It’s important to note that the concept of time doesn’t apply in this unit, it is only a unit of length, it describes how far light can travel in one year but doesn’t say anything about time.
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