Elliptical galaxy NGC 404 lies in the constellation Andromeda, glowing at magnitude 10.3 with a diameter of 6.1′. It carries two other names: Mirach’s Ghost and the Lost Pearl Galaxy. And though the galaxy is well placed for viewing on Halloween night, that’s not how it got the first moniker.
Amateur astronomers call it Mirach’s Ghost because it lies only 6.8′ from 2nd-magnitude Mirach (Beta [β] Andromedae). That makes it easy to locate but, as you can imagine, a 10th-magnitude galaxy next to a star that bright is pretty difficult to see.
Astronomers classify NGC 404 as a lenticular galaxy (or S0 galaxy). This type has the disk shape of a spiral galaxy but no spiral arms. Several teams of researchers have pegged its distance at 10 million light-years from Earth, just outside the Local Group of galaxies.
In 2016, while examining images he took in 2010 and 2013, Italian amateur astronomer Giuseppe Donatiello discovered a dwarf spheroidal galaxy that may be a satellite of NGC 404 (dubbed Mirach’s Goblin). The uncertainty lies in its distance measurements, which stand between 8.1 million and 11.4 million light-years.
To observe Mirach’s Ghost, use high magnification to increase the contrast (and the apparent separation) between the galaxy and the star. NGC 404 is round with a brighter center. The glare from Mirach is troublesome, but there’s really no detail to be seen in the galaxy.
As to NGC 404’s second common name, Astronomy Contributing Editor Stephen James O’Meara christened it the Lost Pearl Galaxy. “Lost” is because some star atlases don’t plot this object, because the printed image of Mirach overlaps it. As for “pearl,” he says it looks like a loose pearl rolling across the deck of a pirate ship.