The star Mirach (Beta Andromedae) in the constellation Andromeda acts as the guide star to three different galaxies: M31 (Andromeda galaxy), M33 (Triangulum galaxy), and NGC 404. When you gaze at this star, it might occur to you that – while Mirach lies at a distance of only 200 light-years – it can aid in finding objects that are millions of light-years away.
Use Mirach to find the Andromeda galaxy (M31). A line drawn from the star Mirach through the star Mu Andromedae escorts you to the Andromeda galaxy. This galaxy is the nearest large spiral galaxy to our Milky Way, and it’s the most distant thing you can see with your eye alone. You need a dark moonless sky to see it with just the eye, though. Click here to read more about the Andromeda galaxy.
Use Mirach to find the Triangulum galaxy (M33). A line drawn in the opposite direction – from the star Mu Andromedae through the star Mirach – takes you in the direction of the Triangulum galaxy. This galaxy is a nearby face-on spiral galaxy, often photographed, but difficult to glimpse with the eye alone. Mirach sits midway between the Andromeda and Triangulum galaxies. Click here to read more about the Triangulum galaxy.
M31 and M33 weren’t recognized as galaxies until the 20th century (1901-2000). Before then, these faint fuzzies were referred to as nebulae. Astronomers in earlier centuries didn’t have telescopes powerful enough to resolve galaxies into individual stars. In the later 18th century (1701-1800), the great comet hunter Charles Messier listed M31 and M33 as masquerade comets in his famous Messier catalogue.
Use Mirach to find Mirach’s Ghost (NGC 404). So where is the third galaxy, sometimes called Mirach’s Ghost or NGC (New General Catalogue) 404? Look at Mirach, and you’re looking almost exactly in the direction of NGC 404. The galaxy lies about one-tenth of one degree from Mirach (the full moon equals one-half degree).
This galaxy is located about 10 million light years away. It apparently lies just beyond our Local Group of galaxies (both the Andromeda and Triangulum galaxies are part of the Local Group) and does not appear gravitationally bound to it. William Herschel was the first to notice Mirach’s Ghost, in the year 1784. Today many amateur astronomers try to spot it with their small telescopes, but – due to its proximity to the star Mirach – seeing the galaxy is not easy.
Bruce McClure has served as lead writer for EarthSky's popular Tonight pages since 2004. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also writes and hosts public astronomy programs and planetarium programs in and around his home in upstate New York.