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astro22

Astronomy distance unit converter

1 AU = 149,597,870.7 km · 1 ly = 63,241 AU · 1 pc = 3.262 ly

The four units astronomers actually use

Kilometers — for distances inside the Earth-Moon system. The Moon orbits at an average 384,400 km.

Astronomical units — for the solar system. Defined exactly as 149,597,870.7 km by the IAU. Neptune's orbit is 30 AU. The Voyager spacecraft passed 150 AU in the late 2010s.

Light-years — for nearby stars. Proxima Centauri at 4.246 ly is the closest. The Milky Way is roughly 100,000 ly across.

Parsecs — for cataloguing distances measured by parallax. Used in research papers. 1 pc ≈ 3.262 ly. Most published distance figures in journals use parsecs or kiloparsecs.