Light-year conversions

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The light-year conversion selector on this page selects the length/distance measurement unit to convert to starting from light-years (ly). To make a conversion starting from a unit of length other than light-year, simply click on the "Reset" button.

What is light-year?

The light-year (also lightyear or light year) is a unit of distance equal to approximately 9.461x1015 meters (1 ly ≈ 9.461x1015 m), the base unit of length in the International System of Units (SI). It is also equal to about 9.461x1012 kilometers (km) (an SI unit of length), or 5.879x1012 miles (mi) or 31.04x1015 feet (ft), which are US customary / Imperial units of length.

The International Astronomical Union (IAU) defines the light-year as the distance that light travels in free space (or vacuum) in one Julian year. In astronomy, the Julian year is defined as having exactly 365.25 days of 86,400 SI seconds each.

The light-year is used in astronomy. Common astronomical measurement units include the parsec (1 ly = 0.306601 pc), the astronomical unit (1 ly = 63.2411x103 AU) and the light-second (1 ly = 31,557,600 light-seconds).

Symbol:

ly

Plural:

light-years

Also known as:

lightyear or light year