Posted by on Aug 30, 2013 in Constellation Of the Month | 0 comments

The stars of Andromeda arc up and to the left of the top left star of the square of Pegasus. (Alpheratz or Alpha Andromedae). Alpheratz is included in the square of Pegasus, and was at one time classified in the Pegasus constellation. The reason for its transfer is not clear. Andromeda consists mainly of a line of fairly bright stars extending from the square of Pegasus towards the constellation of Perseus.

Star Visual Magnitude Spectrum Absolute Magnitude Distance (Lt Years)
MIRACH (ver) 2.07 M0IIIvar -1.86 199
ALPHERATZ 2.07 B9p -0.30 97
ALMAAK 2.10 B8V -3.08 355
ADHIL 4.87 K0III-IV 0.98 195

Almaak is a fine example of a double star. The primary star is yellowish, and in a moderate telescope the companion star can be seen as a bluish fifth magnitude star.

The most dramatic object in this constellation is M31, the Andromeda Nebula. It is a great spiral galaxy, similar to, but somewhat larger than, our galaxy and lies about 2.5 million light years from us. It can be seen with the naked eye as a faint elliptical glow as long as the sky is reasonably clear and dark. Not far from the 4.5 magnitude star Andromeda ‘v’. Binoculars or a small telescope will show it clearly. It is a bit disappointing as it does look like a faint fuzz of light in anything but a large telescope.

Move up and to the left two stars from Sirra, these are Pi and Mu Andromedae. Then move your view through a right angle to the right of Mu by about one field of view of a pair of binoculars and you should be able to see it easily. M31 contains about twice as many stars as our own galaxy, the Milky Way, and together they are the two largest members of our own Local Group of about 3 dozen galaxies.

In November, the Andromedids meteor shower appears to radiate from this constellation.

M31 (NGC 224)

The Andromeda Galaxy is one of the most distant objects visible to the naked eye, 2.2 million light-years from Earth (estimates range up to 2.5 million light-years); it is seen under a dark, transparent sky as a hazy patch in the north of the constellation M31 is the largest neighbouring galaxy to the Milky Way, and the largest member of the local group of galaxies. In absolute terms, M31 is approximately 200,000 light-years in diameter, twice the size of the Milky Way. It is an enormous – 192.4 by 62.2 arcminutes in apparent size. It is a barred spiral galaxy similar in form to the Milky Way, and at an approximate magnitude of 3.5, is one of the brightest deep-sky objects in the northern sky. Despite being visible to the naked eye, the “little cloud” near Andromeda’s figure was not recorded until 964, when the Arab astronomer Arab astronomer Al-Sufi wrote his ‘Book of fixed stars’. M31 was first observed telescopically shortly after its invention, by Simon Marius in 1612. M31 is often referred to as a twin sister to the Milky Way, but it has only half the mass of the Milky Way despite being twice its diameter. The futures of the Andromeda and Milky Way galaxies may be interlinked: in about five billion years, the two could potentially begin a collision that would spark extensive new star formation. American astronomer Edwin Hubble included M31 (then known as the Andromeda Nebula) in his groundbreaking 1923 research on galaxies. Using the 100-inch Hooker telescope at Mount Wilson observatory in California, he observed Cepheid variable stars in M31 during a search for novae, allowing him to determine their distance by using the stars as standard candles The distance he found was far greater than the size of the Milky Way, which led him to the conclusion that many similar objects were “island universes” on their own.

M32 (NGC 221) and M110 (NGC 205)

The Andromeda Galaxy’s two main companions, M32 and M110 (also known as NGC 221 and NGC 205, respectively) are faint elliptical galaxies that lie near it. M32, visible with a far smaller size of 8.7 by 6.4 arcminutes, compared to M110, appears superimposed on the larger galaxy in a telescopic view as a hazy smudge, and M110 appears slightly larger and distinct from the larger galaxy. M32 is 0.5° south of the core, and M32 is 1° northwest of the core. M32 was discovered in 1749 by French astronomer Guillaune Le Gentil, and has since been found to lie closer to Earth than the Andromeda Galaxy itself. It is viewable in binoculars from a dark site owing to its high surface brightness of 10.1 and overall magnitude of 9.0. M110 is classified as either a dwarf spheroidal galaxy or simply a generic elliptical galaxy. It is far fainter than M31 and M32, but larger than M42 with a surface brightness of 13.2, magnitude of 8.9, and size of 21.9 by 10.9 arcminutes. The Andromeda Galaxy has a total of 15 satellite galaxies, including M32 and M110. Nine of these lie in a plane, which has caused astronomers to infer that they have a common origin. These satellite galaxies, like the satellites of the Milky Way, tend to be older, gas-poor dwarf elliptical and dwarf spheroidal galaxies.

NGC 891

Along with the Andromeda Galaxy and its companions, the constellation also features NGC 891 a smaller galaxy just east of Almaak. It is a barred spiral galaxy seen edge-on, with a dark dust lane visible down the middle. NGC 891 is incredibly faint and small despite its magnitude of 9.9, as its surface brightness of 14.6 indicates; it is 13.5 by 2.8 arcminutes in size. The brother-and-sister team of William and Caroline Herschel discovered it in 1783. This galaxy is at an approximate distance of 30 million light years from Earth, calculated from its redshift of 0.002.

NGC 752

Andromeda’s most celebrated open cluster is NGC 752, at an overall magnitude of 5.7, It is a loosely scattered cluster in the Milky Way that measures 49 arcminutes across and features approximately twelve bright stars, although more than 60 stars of approximately 9th magnitude become visible at low magnifications in a telescope. It is considered to be one of the more inconspicuous open clusters.

NGC 7686

The other open cluster in Andromeda is NGC 7686, which has a similar magnitude of 5.6 and is also a part of the Milky Way. It contains approximately 20 stars in a diameter of 15 arcminutes, making it a tighter cluster than NGC 752.

NGC 7662

There is one prominent planetary nebula in Andromeda. NGC 7662 (Caldwell 22). Lying approximately three degrees southwest of Lota Andromedae at a distance of about 4,000 light-years from Earth, the “Blue Snowball Nebula” is a popular target for amateur astronomers. It earned its popular name because it appears as a faint, round, blue-green object in a telescope, with an overall magnitude of 9.2. Upon further magnification, it is visible as a slightly elliptical annular disk that gets darker towards the centre, with a magnitude 13.2 central star. The nebula has an overall magnitude of 9.2 and is 20 by 130 arcseconds in size.