Andromeda I, or And 1, is a dwarf spheroidal galaxy (dSph). It is a satellite of the Andromeda Galaxy and is in the constellation of Andromeda. It is roughly 3.5 degrees south and slightly east of the Andromeda Galaxy. It is 3 million light years away.

And 1 was discovered by Sydney van Der Bergh in 1970 with the Mount Palomar Observatory 48-inch telescope. Further study of And 1 was done by the WFPC2 camera of the Hubble Space Telescope. This found that the horizontal branch stars, like other dSph galaxies were predominately red. From this, and the abundance of blue horizontal branch stars, along with RR Lyrae stars, lead to the conclusion there was an extended epoch of star formation. The estimated age is approximately 10 Gyr . The Hubble telescope also found a globular cluster in And 1, being the least luminous galaxy where such a cluster was found.

References

• SEDS article on And 1
• Grebel, E. K.; Dolphin, A. E.; Guhathakurta, P. Discovery of a Globular Cluster in M31's Dwarf Spheroidal Companion Andromeda I (2000) The Publications of the Astronomical Society of the Pacific, Volume 112, Issue 770, pp. 529-536.
• Da Costa, G. S.; Armandroff, T. E.; Caldwell, Nelson; Seitzer, Patrick. The Dwarf Spheroidal Companions to M31: WFPC2 Observations of Andromeda I (1996) Astronomical Journal v.112, p.2576
• van den Bergh, Sidney. Search for Faint Companions to M31 (1972). Astrophysical Journal, vol. 171, p. L31-L33
• van den Bergh, Sidney. Updated Information on the Local Group. (2000) PASP, Vol. 112, No. 770, p. 529-536