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Calendar of astronomy, November sky

Constellation Andromeda

 Automatic translationAutomatic translation Category: children
Updated January 21, 2013

During the autumn season, we can identify in the sky of the northern hemisphere, the great square of Pegasus constituted by Markab (α Peg), Sheat (β Peg) and Algenib (γ Peg), of the constellation of Pegasus Alpheratz or Sirrah (and α), of the constellation of Andromeda. The great square of Pegasus is a major reference of the celestial sphere due to its square shape, three times bigger than the Great Bear. The constellation Andromeda contains three bright stars whose names are of Arabic origin. It is Alpheratz or Sirrah (And α), Mirach (β And) and Almach (γ And). Alpheratz is a bluish white star 200 times more luminous than our Sun. Almach, formerly included in Pegasus, is actually a pair of stars in contrasting colors, orange and blue, one is orange, the other is blue. About Mirach, the red giant at the end of life, it will help the observer to find the beautiful galaxy M31if his look prolongs to the northwest. Evening to east, this constellation is easily visible to the naked eye when the night sky is very pure. In the constellation Andromeda, but further in the cosmos, a distance of 2.5 million light-years away, it is a beautiful galaxy. it is Andromeda or Messier 31, the nearest galaxy to our own, it contains about 400 billion stars.


nota: A constellation is a group of stars that sufficiently close to the celestial vault are gave the appearance of an imaginary figure drawn in the sky.

nota: By convention, the names of the stars in a constellation are prefixed by a Greek letter followed by the first 3 letters of the constellation, for example:
α  Ori, β Ori,... (Greek letters: α β γ δ ε ζ η θ ι κ λ μ ν ξ ο π ρ ς σ τ υ φ χ ψ ω).

nota: a light year is exactly 9 460 895 288 762 850 meters.

nota: M is the mark of the Messier catalog, a catalog of astronomical objects look like diffuse nebulae or galaxies.

Image: Constellation Andromeda. Image reworked from the Open Source software Stellarium.

 Constellation Andromeda

Andromeda galaxy or M31 or NGC 224


The Andromeda Galaxy is the closest large neighboring galaxies to our own Milky Way. It is probable that our galaxy, the Milky Way, is very similar to the Andromeda galaxy. The Great Andromeda Galaxy and the Milky Way are the two largest galaxies in the Local Group. The galaxy M31 is the 31st entry in the catalog of diffuse sky objects, established by the French astronomer Charles Messier. M31 is about 2.5 million light years from our galaxy, i.e. that its light takes 2.5 million years to reach us. This galaxy is one of the few galaxies visible to the naked eye, when the climatic conditions are favorable. Its apparent diameter is pretty huge because it is equivalent, as seen from Earth to 5 full moon diameters. Its real diameter is 170,000 light-years. The two "universe island", the Milky Way and Andromeda are approaching each other at a speed of about 300 km/s and could collide in a few billion years. This hypothesis unconfirmed, remain probable. The Milky Way and the Great Andromeda Nebula have both satellite galaxies. These two giant spirals belong to a group still bigger called the Local Group with more than 20 galaxies with M33, Maffei I and II Maffei, the Large and Small Magellanic Cloud. The local group is part of a huge complex of 10  000 galaxies assembled in clusters spanning some 200 million light years away, called Local Supercluster or Virgin Supercluster.

nota: M is the mark of the Messier catalog, a catalog of astronomical objects look like diffuse nebulae or galaxies.


Video: Andromeda constellation.

nota: NGC (New General Catalogue) is one of the most popular catalogs in the field of astronomy with the Messier catalog.

nota: A (Abell catalog of clusters of galaxies). It is a catalog published in 1958 by George Abell (1927 - 1983) which lists 4073 clusters of galaxies.
 galaxie d'andromède ou M31

Image: Galaxy M31 has an apparent magnitude of 3.38 making it visible to the naked eye. The glow of Andromeda is none other than the light accumulated hundreds of billions of stars that compose it. The stars we see in the foreground of this image are actually stars in our own galaxy. At the bottom right you can see his companion, the dwarf galaxy NGC 205 or M110. The big bright spot 10 H very close to the disk of M31 is M32 another companion galaxy. Credit: Robert Gendler (

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