Andromeda

Andromeda galaxy is the nearest major galaxy to the milky way and is cataloged as Messier 31, M31 and NGC 224. Its original name was Andromeda Nebula</nowiki> and the name was originated from the wife of Perseus, princess Andromeda from Greek mythology. Andromeda galaxy can be seen with naked eyes, but it is only possible on the moonless nights.

The first person ever to discover and describe the Andromeda galaxy with naked eyes were the Persian astronomer Abd al-Rahman al-Sufi around the year 964 CE. He referred it as a "nebulous smear" or "small cloud" in his book. And the first person to give a description of the Andromeda galaxy were German astronomer Simon Marius in year 1612 followed by fellow European astronomer Pierre Louis Maupertuis in 1745. Charles Messier cataloged Andromeda as object M31 in 1764 and incorrectly credited Marius as the discoverer.

In 1850, the first drawing of Andromeda's spiral structure was made by astronomer William Parsons, 3rd Earl of Rosse.

In the year 1864, William Huggins noted that the spectrum of Andromeda differed from that of a gaseous nebula. Isaac Roberts took one of the first photographs of Andromeda in 1888, which is still commonly thought to be a nebula within our galaxy.

A major collision of 2 galaxies occurred 2 to 3 billion years ago at the current Andromeda location, which the galaxies' mass ratio were approximately 4. The discovery of a recent merger in the Andromeda galaxy was first based on interpreting its anomalous age-velocity dispersion relation, as well as the fact that 2 billion years ago, star formation throughout Andromeda's disk was much more active than today.

Based on its appearance in visible light, the Andromeda galaxy can be classified as an SA(s)b galaxy based on the de Vaucouleurs–Sandage extended classification system. However, infrared data from the 2MASS survey and the Spitzer Space Telescope showed that Andromeda is actually a barred spiral galaxy, like the Milky Way.

As you might know, space expands constantly. But it's not the case between the Milky way and the Andromeda galaxy. Andromeda galaxy is currently 2.537 million light years away from us. But there's a lot of studies showing that the Milky way and Andromeda is colliding in about 4.5 billion years from now on.