# Light year

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A light year is the distance light travels in one year in a vacuum. It is a measure of distance used in popular science for distances to great too express in kilometers or miles.

Professional astronomers prefer to use the parsec (approximately 3.26 light years) instead of the light year.

The light year is easily derived from the speed of light which is about 300,000,000 meters per second = m/s.

A light year can then be calculated to be about m/s times 3600s times 24 times 365 =  kilometers, or  miles (5900 billion miles).
(To put this in perspective: a person would have to live 31 years, 251 days, 7 hours, 46 minutes, and 39 seconds to reach the age of 1 billion seconds-old.)[1]

The distance in light years is equal to the time a light wave needs to cover that distance[2] . Many objects in the universe are more than 10,000 light years away, giving rise to the starlight problem as well as the Horizon Problem in the Big Bang Model of the Universe.

## References

1. http://mathforum.org/library/drmath/view/58739.html
2. Wile, Dr. Jay L. Exploring Creation With Physical Science. Apologia Educational Ministries, Inc. 1999, 2000