Space · Distance
Light-year, AU and parsec converter.
Type a distance in any astronomical unit and read it in all the others.
Inputs
Converted distances
Enter a distance.
How the three astronomical units relate
The astronomical unit (AU) is defined as exactly 149,597,870,700 m (IAU 2012). A light-year is the distance light travels in a Julian year of 365.25 days at 299,792,458 m/s, which gives 9,460,730,472,580,800 m. A parsec is defined as exactly 648,000 / pi AU, about 30.857 trillion km.
Worked example. 1 light-year = 63,241 AU = 9.4607 trillion km = 5.8786 trillion miles = 0.30660 parsecs. In the other direction, 1 parsec = 3.26156 light-years = 206,265 AU.
Professional astronomers mostly use parsecs, while popular science writing uses light-years. An AU is handy inside the solar system: Earth is 1 AU from the Sun.
Frequently asked questions
How many AU are in a light-year?
About 63,241 AU.
How many light-years are in a parsec?
About 3.2616 light-years.
How many kilometres are in a light-year?
About 9.4607 trillion km (9,460,730,472,580.8 km using a 365.25-day Julian year).
Do other sources give a slightly different light-year?
Yes. A value near 9.4605 x 10^15 m uses a 365.2425-day Gregorian year instead. This tool follows the IAU Julian-year definition.
Sources
Checked
- NASA JPL Solar System Dynamics: Astrodynamic Parameters
- Wikipedia: Light-year (IAU definition from the Julian year)
- Wikipedia: Parsec (IAU 2015 Resolution B2 definition)
- NIST CODATA: speed of light in vacuum
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Scope
Conversion of defined units. It does not measure the distance to any real object.