What Is a Light Year?

Significance

• The great distances that need to be described in outer space made the light year a much more practical measurement than miles. Using miles to describe how far it was to a certain star would be the equivalent of using inches to measure the distance between the North and South Poles.

Calculations

• Light moves at the speed of 186,000 miles per second through space. To calculate the distance in a light year in miles you need to multiply that figure by the 3,600 seconds in an hour by the 24 hours in a day and then that total by 365 days in a year.

Proxima Centauri

• The closest star besides the Sun to Earth is Proxima Centauri, which is 4.2 light years distant from our planet. The light that a person observes from this star began its trip towards her eye 4.2 years ago.

Light minutes

• The distance that light can travel in a single minute is 11 million miles. Astronomers will use these smaller "light minutes" to describe distances within our own solar system.

Astronomical unit

• The distance from the Earth to the Sun is about 93 million miles and is referred to as an astronomical unit. This means that one light year equals over 63,239 astronomical units.