Mpc
megaparsec
Lengthexact by definition
A megaparsec is one million parsecs, about 3.086 × 10²² metres or 3.26 million light-years. It is the unit of extragalactic distance: the Andromeda galaxy is 0.78 Mpc away, the Virgo cluster about 16.5 Mpc, and the Hubble constant is quoted in kilometres per second per megaparsec.
Watch out: The Hubble constant's units, km/s/Mpc, hide a pure reciprocal time. Converting the megaparsec to kilometres turns H₀ ≈ 70 into about 2.3 × 10⁻¹⁸ s⁻¹, whose inverse is the Hubble time of roughly 14 billion years.
| 1 Mpc | 3.0856776e+22 m |
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