Gems of the sky - The galaxy in Andromeda

[glactus]

Andromeda

The Andromeda Galaxy, Messier 31, is a spiral galaxy approximately 2.5 million light-years away in the constellation of Andromeda and is the nearest spiral galaxy to our own, the Milky Way. As it is visible as a faint smudge on a moonless night, it is one of the farthest objects visible to the naked eye, and can be seen with binoculars even in urban areas.

Andromeda is the largest galaxy of the Local Group, which consists of the Andromeda Galaxy, the Milky Way Galaxy, the Triangulum Galaxy, and about 30 other smaller galaxies.

Although the largest, it may not be the most massive, as recent findings suggest that the Milky Way contains more dark matter and may be the most massive in the grouping. However, recent observations by the Spitzer Space Telescope revealed that M31 contains one trillion stars, greatly exceeding the number of stars in our own galaxy. The 2006 estimates put the mass of the Milky Way to be 80% of the mass of Andromeda,

At an apparent magnitude of 4.4, the Andromeda Galaxy is notable for being one of the brightest Messier objects, making it easily visible to the naked eye even when viewed from areas with moderate light pollution. It appears quite small without a telescope because only the central part is bright enough to be visible, but the full angular diameter of the galaxy is seven times that of the full moon.



Credits: Andromeda galaxy image by NASA

[Andy Mac]

As you say Henry, this galaxy is best observed with either a rich field telescope or decent pair of binoculars. Alot of newcomers to the hobby find this galaxy to be rather disappointing - especially when observed from an urban location where only the bright central core is visible as a 'smudge'.

Imaging it properly is also a challenge as the central core is so much brighter than the outer reaches. The trick is to combine short and long exposures together to bring out faint outer arm & dust lane detail - but without the core appearing too overexposed and burnt out.