M31, the Andromeda Galaxy, is among the most distant objects visible to the naked eye. M31 is a spiral galaxy, a star city shining with the brilliance of more than 200 billion suns. Despite its distance of about 2.4 million light-years, the Andromeda Galaxy is easily seen without optical aid from a typical rural location. When you find M31, bear in mind that the light you are seeing has been travelling through space for more than two million years, since before modern man walked the Earth.
Your search for M31 begins in Pegasus, the winged horse of ancient mythology. This region is often identified by an arrangement of four bright stars. Scheat, Markab, Algenib and Alpheratz form the Great Square asterism. All but one belong to Pegasus. Alpheratz, the star marking the northeast corner of the Great Square, actually resides in Andromeda. Andromeda is distinguished by two rows of stars arching to the northeast from Alpheratz. The bottom row features brighter stars, including Delta and Beta Andromedae. Beta Andromedae, more commonly referred to as Mirach, is the second star you encounter along Andromeda's southern row. Jump from Mirach to the nearest star in the second row. This is 3.9 magnitude Mu Andromedae and it is just 3.8 degrees from Mirach. Continue in the same direction for 3.7 degrees and you should glimpse a delicate, elongated patch of light. That's not a cloud. That's M31, the Andromeda Galaxy.
| Autumn Sky Tour: M31-The Andromeda Galaxy (Andromeda) RA: 00h 42.7m / DEC: +41° 16'.1 |
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Revised: February 10, 2002 [WDF]
M31 shines at magnitude 4.4 and is an easy naked eye object from a dark sky site. My favorite view is through wide field binoculars. However, the view through my Starfinder Newtonian is also pleasing. My sketch renders the view in the 10-inch at 36X. The true field of view is about 90 arc minutes. M31 is visible as a swath of nebulosity cutting a path northeast to southwest through the field. It features a stellar nuclear region within a 15'x6' core. This is encased within the glow of more than 200 thousand-million stars appearing as a gauzy halo spilling beyond the boundaries of the eyepiece. M32, a satellite galaxy of M31, is visible 21' south of M31. M32 is a magnitude 8.0 elliptical galaxy, 4' in diameter, with a bright core. M110 is seen just inside the northern edge of the field. This elliptical galaxy covers a 15'x6' area and is the most difficult of the three to detect.