Light-year

Definition

A light-year is the distance that light travels in one year in a vacuum, approximately 5.88 trillion miles (9.46 trillion kilometers). It is commonly used to measure distances between stars and other celestial objects.

5 Must Know Facts For Your Next Test

1. A light-year measures distance, not time.
2. Light travels at a speed of about 186,282 miles per second (299,792 kilometers per second).
3. The nearest star to Earth, Proxima Centauri, is about 4.24 light-years away.
4. Light-years help astronomers understand the scale of the universe and the positions of stars relative to each other.
5. The concept of a light-year helps in determining how far back in time we are looking when observing distant celestial objects.

Review Questions

• What does a light-year measure?
• How far does light travel in one year?
• Why are light-years useful for astronomers?

Related terms

Parsec:

A unit of distance equal to about 3.26 light-years or approximately 19 trillion miles (31 trillion kilometers).

Astronomical Unit (AU): The average distance from the Earth to the Sun, roughly about 93 million miles (150 million kilometers).

Redshift:

The phenomenon where light from an object moving away from the observer is increased in wavelength, or shifted to the red end of the spectrum, often indicating cosmic distances and speeds.