Light Year Calculator
Kilometers
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Miles
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Astronomical Units
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Parsecs
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Understanding Cosmic Distance Units
A light year is the distance light travels in one year: about 9.461 trillion km. The nearest star, Alpha Centauri, is 4.37 light years away.
An astronomical unit (AU) is the Earth-Sun distance: 149.6 million km. One light year equals about 63,241 AU.
A parsec equals 3.26 light years. Defined by stellar parallax: distance where 1 AU subtends 1 arcsecond.
Frequently Asked Questions
How far is one light year?
About 9.461 trillion km or 5.879 trillion miles. Light travels at 299,792 km/s.
Nearest star?
Proxima Centauri at 4.24 light years. Alpha Centauri A/B at 4.37 light years.
What is a parsec?
3.2616 light years or 30.86 trillion km. Based on trigonometric parallax.
Size of observable universe?
Radius about 46.5 billion light years. Most distant visible galaxies about 13.4 billion light years away.