Constellations for October 2022 - Pegasus and Andromeda
Pegasus (the flying horse) and Andromeda are two ancient constellations based on Greek mythology. In the autumn evening if you look south you will see a line of four bright stars about a third of the way up the sky. Going from west (i.e. right) to east (left), they are Scheat, Alpheratz, Mirach, and Almach. Scheat and Alpheratz are the two top stars in the famous Square of Pegasus, and beneath them are Markab and Algenib which form the bottom edge of the Square of Pegasus, marked by yellow lines in the chart below.
The number of stars you can see within the square is a measure of light pollution. If you can see more than four stars, you are doing very well! Enif is a bright star between the Square of Pegasus and the small constellation of Equuleus. Just above Enif using binoculars you can see the globular cluster Messier 15 [1]; it is 33,000 light years away and 12 billion years old. Enif is known as the Pendulum Star. It is a wide double with a bright yellow star with a dim blue companion. If you knock your telescope slightly, the telescope wobbles and the dim star wobbles with it, but thanks to the phenomenon of the persistence of vision, it seems to stay fixed. If the dim star is below the main star, this looks like the pendulum of a clock.
To the west of the square (in other words, to the right), about roughly halfway between Scheat and Markab, there is a 5.5 magnitude star originally called 51 Pegasi [2], but now officially named Helvetios. In 1995, the Swiss astronomers Michel Mayor and Didier Queloz discovered the first planet, a hot Jupiter, orbiting a normal star, 51 Pegasi.
Using binoculars (or a telescope), go to Mirach and then go up two dimmer stars; you will then be able to see the silver disc of the Andromeda Galaxy [3], which is the closest large galaxy to our Milky Way, though still 2.5 million light years away. In a dark area, without light pollution, you can see the Andromeda Galaxy with the naked eye – it is the most distant object we can see using just our eyes.
Almach is a double star with a yellow primary (magnitude 2.3) and a blue secondary (mag. 5.0) with a fairly easy separation of 9.8 arcseconds. Between Almach and Mirach (but lower down) is the wide double 57 Andromedae [4], which are almost equal in brightness (5.8 and 6.1) with a separation of 203 arcseconds. It is next to the star cluster NGC 752 and with the addition of four stars which make up the shaft, they form the Golf Putter asterism.
Above the Square of Pegasus there are two interesting objects which are actually within the boundary of Andromeda. Z Andromedae [5], just below the inconspicuous star cluster NGC 7686, is an 8th magnitude cataclysmic variable star, a binary system in which matter is transferred from a red giant to a white dwarf which flares up roughly every twenty years. Between NGC 7686 and Alpheratz is the Blue Snowball [6] planetary nebula, which is Caldwell 22 (and NGC 7662). In a small telescope it is a fuzzy blue dot, but a larger telescope will show a small disc.
