Andromeda galaxy, definition and study. A-Z index of Cognitio.

The Andromeda Galaxy is a giant spiral galaxy part of the Local Group, along with the Milky Way; is about 2,538 million light years from Earth, in the direction of the Andromeda boreal constellation, from which it is named.

Constellation, definition and study. A-Z index of Cognitio.


This is the large spiral galaxy closest to our galaxy; is also visible to the naked eye and it is the farthest object visible from human eyes without the help of observation tools. 

The Andromeda Galaxy is the largest in the Local Group, a group of galaxies formed by the Milky Way, Andromeda and the Triangle Galaxy, plus some fifty other minor galaxies, many of which are major satellites. Though it is the largest, it seems to be not the most massive, as some studies suggest that the Milky Way contains more obscure matter and could be that with the largest mass of the group.

Dark matter, definition and study. A-Z index of Cognitio.

Dark matter

The Andromeda Galaxy finds itself extremely easy: once the constellation of membership and in particular the Mirach star is identified, proceed to the northwest direction following the alignment of the stars Andromedae and Andromedae towards NE / SW between Perseus and Pegasus, in order to identify a mud-shaped stain, stretched in the Northeast-southwest direction; you can also notice it with a naked eye if the sky is in optimal condition and without light pollution. 

Alignment, definition and study. A-Z index of Cognitio.


The first observation of the Andromeda Galaxy in writing dates back to 964 and was conducted by Persian astronomer Abd al-Rahmān al-Sūfi, who described it as a “little cloud” in his fixed star book. In 1885, a supernova was observed in the M31 aliens, cataloged as S Andromedae, the first and the only one observed so far in the galaxy; at the time when M31 was considered a “close” object, it was believed that this was a much less luminous event, called nova, so it was referred to as “Nova 1885”.

Nova, definition and study. A-Z index of Cognitio.


Yet it was still believed that it was a nebula contained in our Galaxy and it was mistakenly thought that it was a spiral cloud in which systems similar to our solar system were formed, where the clouds of satellites would be planets in formation.

The dilemma was resolved in 1925, when for the first time some Cepheid variables were identified in some photos of the galaxy created in the Monte Wilson Observatory, thus making the measurement of distance much more accurate; its measurements in fact demonstrated unequivocally that M31 is an independent galaxy located at considerable distance from our. The Andromeda Galaxy is approaching the Milky Way at a speed of about 300 km / s, so it is one of the few galaxies to show a blue shift; given the movement of the Sun within our Galaxy, it turns out that the two galaxies approach the speed of 100-140 km / s.

Sun, definition and study. A-Z index of Cognitio.


The two galaxies could thus collide in an estimated time of 2.5 billion years: in that case they will probably merge, giving rise to an elliptical galaxy of great proportions. The Andromeda Galaxy is home to a very dense and compact star of its kind in its center; in large telescopes it is possible to observe the stars immersed in the surrounding diffuse bulge. The luminosity of the core exceeds that of the brightest globular clusters.

Andromeda galaxy, definition and study. A-Z index of Cognitio.



To open the video  click on the image, good view from your Alessandro Brizzi.

Andromeda galaxy, definition and study. A-Z index of Cognitio.

Andromeda galaxy