An Etymological Dictionary of Astronomy and Astrophysics
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A small → dwarf irregular galaxy belonging to the → Local Group, which is located in the constellation → Cassiopeia. IC 10 is about 2.3 million light-years distant and about 5,000 light-years across. With an absolute B magnitude of -16.5, IC 10 has an integrated luminosity that is comparable to that of the → Small Magellanic Cloud, although it is considerably smaller. Its → metallicity is roughly a factor of 2 higher than that of the SMC and in the same proportion smaller than → LMC's. Compared to other Local Group galaxies, IC 10 has a large population of newly formed stars that are massive and intrinsically very bright, especially → Wolf-Rayet stars. Its W-R star density is larger than those of the LMC and SMC. Moreover, the relative number of known → WC to → WN type Wolf-Rayet stars is unusually high, which is unexpected for IC 10's metallicity. IC 10 is also known to be unusual in having → H I gas that extends about 7 times the optical dimensions of the galaxy. IC 10 is the nearest example of a → starburst galaxy. IC 10 was discovered by the American astronomer Lewis A. Swift (1820-1913) in 1887.

Number 10 in the → Index Catalogue.