Andromeda I
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Andromeda I is a dwarf spheroidal galaxy (dSph)<ref name="Bergh1972">Template:Citation</ref> about 2.40<ref name="McConnachieetal2004" /> million light-years away in the constellation Andromeda. Andromeda I is part of the local group of galaxies and a satellite galaxy of the Andromeda Galaxy (M31). It is roughly 3.5 degrees south and slightly east of M31.<ref name="seds">Template:Citation</ref> As of 2005, it is the closest known dSph companion to M31<ref name="Pritzletal2005">Template:Citation</ref> at an estimated projected distance of ~40<ref name="McConnachieetal2004">Template:Citation</ref> kpc or ~150,000<ref name=seds /> light-years.
Andromeda I was discovered by Sidney van den Bergh<ref name="McConnachieetal2005">Template:Citation</ref> in 1970 with the Mount Palomar Observatory 48-inch telescope.<ref name="Bergh1972" /> Further study of Andromeda I was done by the WFPC2 camera of the Hubble Space Telescope. This found that the horizontal branch stars, like other dwarf spheroidal galaxies were predominantly red.<ref name="DaCostaetal1996">Template:Citation</ref> From this, and the abundance of blue horizontal branch stars, along with 99 RR Lyrae stars detected in 2005,<ref name="Pritzletal2005" /> lead to the conclusion there was an extended epoch of star formation. The estimated age is approximately 10 Gyr. The Hubble Space Telescope also found a globular cluster in Andromeda I, being the least luminous galaxy where such a cluster was found.<ref name="Grebeletal2000">Template:Cite book</ref>
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