Andromeda Galaxy - Observation History

Observation History

The Persian astronomer Abd al-Rahman al-Sufi wrote a tantalizing line about the chained constellation in his Book of Fixed Stars around 964, describing it as a "small cloud". Star charts of that period have it labeled as the Little Cloud. The first description of the object based on telescopic observation was given by German astronomer Simon Marius on December 15, 1612. Charles Messier catalogued it as object M31 in 1764 and incorrectly credited Marius as the discoverer, unaware of Al Sufi's earlier work. In 1785, the astronomer William Herschel noted a faint reddish hue in the core region of the M31. He believed it to be the nearest of all the "great nebulae" and based on the colour and magnitude of the nebula, he incorrectly guessed that it was no more than 2,000 times the distance of Sirius.

William Huggins in 1864 observed the spectrum of M31 and noted that it differed from a gaseous nebula. The spectra of M31 displayed a continuum of frequencies, superimposed with dark absorption lines that help identify the chemical composition of an object. The Andromeda nebula was very similar to the spectra of individual stars, and from this it was deduced that M31 had a stellar nature. In 1885, a supernova (known as S Andromedae) was seen in M31, the first and so far only one observed in that galaxy. At the time M31 was considered to be a nearby object, so the cause was thought to be a much less luminous and unrelated event called a nova, and was named accordingly "Nova 1885".

The first photographs of M31 were taken in 1887 by Isaac Roberts from his private observatory in Sussex, England. The long-duration exposure allowed the spiral structure of the galaxy to be seen for the first time. However, at the time this object was still commonly believed to be a nebula within our galaxy, and Roberts mistakenly believed that M31 and similar spiral nebulae were actually solar systems being formed, with the satellites nascent planets. The radial velocity of this object with respect to our solar system was measured in 1912 by Vesto Slipher at the Lowell Observatory, using spectroscopy. The result was the largest velocity recorded at that time, at 300 kilometres per second (190 mi/s), moving in the direction of the Sun.