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Line 1: − The distance light travels in one year.<ref>Wile, Dr. Jay L. ''Exploring Creation With Physical Science''. Apologia Educational Ministries, Inc. 1999, 2000</ref>+ + + + + + + + + + − <references/>+ + + +
Tidy up formatting of numbers and wikify
A '''light year''' is the distance [[light]] travels in one year in a [[vacuum]].<ref>[https://www.britannica.com/science/light-year Light-year] from britannica.com</ref> It is a measure of [[distance]] used in popular science for distances to great too express in kilometers or miles.
Professional [[astronomer]]s 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 = 3×10<sup>8</sup> m/s.
Since there are 31,536,000 seconds in one year, a light year can then be calculated to be about 3×10<sup>8</sup> m/s × 31536000 s = 9.46×10<sup>12</sup> km, or 5.9×10<sup>12</sup> miles (5900 billion miles).<br>
(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.)<ref>http://mathforum.org/library/drmath/view/58739.html</ref>
The distance in light years is equal to the time a light wave needs to cover that distance.<ref>Wile, Dr. Jay L. ''Exploring Creation With Physical Science''. Apologia Educational Ministries, Inc. 1999, 2000</ref> Many objects in the universe are more than 10,000 light years away, giving rise to the [[starlight problem]] in [[Creation science]]. A similar problem occurs (the [[Horizon problem]]) in the [[Big bang theory|big bang model]] of the Universe. In the [[Big bang theory]], this problem is resolved by the fact the universe is expanding.
==References==
==References==
{{reflist}}
[[Category:Astronomy]]
[[Category:Units of Measurement]]