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. A line drawn from Mirach through Mu Andromedae escorts you to the Andromeda galaxy. A line drawn in the opposite direction, from Mu Andromedae through Mirach, takes you in the direction of the Triangulum galaxy. Mirach sits midway between these two major galaxies.
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. After a period of time, any solar system object – such as a comet – will change its position relative to the backdrop stars, but objects outside the solar system will not.
So where is the third galaxy, NGC (New General Catalogue) 404? Look at Mirach, and you’re looking almost exactly in the direction of NGC 404. Sometimes, this galaxy goes by the nickname “Mirach’s Ghost” because it lies about one-tenth of one degree from this star. (For reference, the diameter of the full moon equals one-half degree.)
Image credit: thebadastronomer
The modern-day comet hunter David Levy lists this galaxy as Levy 64 in his book Deep Sky Objects. He explains that two talented observers – Jim Scotti and Dean Koenig – independently found this galaxy, both thinking they might have discovered a comet. David Levy decided it was high time to red flag this impostor as Levy 64!
Mirach lies at a distance of 200 light-years and NGC 404 at about 10 million light-years.