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Distances in space

Package: UOM_PACKAGE. Registered by createEngine(); for a slimmer engine, register it explicitly (see choosing packages).

Distances in space are too large for kilometres to read comfortably, so astronomy has its own lengths. The astronomical unit (AU) is roughly the distance from the Earth to the Sun and suits the solar system. The light-year (ly) is how far light travels in a year and suits the nearest stars. The parsec (pc), about 3.26 light-years, is the one astronomers measure star distances in. All three are lengths, so they convert to each other and to kilometres or miles.

1 AU in km // 149,597,870.70 km
1 AU in miles // 92,955,807.27 miles
5.2 AU in km // 777,908,927.64 km
1 ly in AU // 63,241.08 AU
1 pc in ly // 3.26 ly

The astronomical unit is the International Astronomical Union’s fixed figure, exactly 149,597,870,700 metres. The light-year and the parsec are the unit table’s own values.

The boundary

Only the capitals AU are the astronomical unit. The IAU’s own lower-case symbol au is not read, because it is also the start of au pair and au revoir, and a number in front of it would turn those into a distance.