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Calendar of astronomy, October sky

Constellation Pegasus

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Updated January 21, 2013

During the autumn season, we can locate in the sky of the northern hemisphere, the large square formed by the constellation Pegasus, to orient among the stars. The constellation Pegasus is located outside the center of the Milky Way and that is why its stars become detached so clearly against the dark sky of autumn. The brightest star in Pegasus is called Markab (α Peg) and it is located on the lower right corner of the large celestial square. Other stars of the constellation Pegasus are Schedar (β Peg) Enif (ε Peg), Biham (θ Peg) Algenib (γ Peg), Matar (η Peg). This constellation is named after Pegase, the winged horse, one of the most famous fantasy creatures from Greek mythology. The constellation Pegasus was listed from the first century AD by Ptolemy in his Almagest and cataloged by William Herschel in 1783. The large square is a major reference of the celestial sphere, which is recognized directly in its form, and the absence of significant star in its scope. In the constellation Pegasus, but further into the cosmos, a distance of 46 million light-years away, there is a galaxy cluster NGC 7331 and the small group Deer Lick.


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 Pegasus. Image reworked from the Open Source software Stellarium.

 Constellation Pegasus

Galaxy NGC 7331, Deer Lick group


The galaxy NGC 7331 has a diameter of 100 000 s, which is the main galaxy of a group of galaxies known as the Deer Lick Group, located 46 million light-years away in the constellation Pegasus the northern hemisphere. NGC 7331 was early identified as a "spiral nebula" as it is one of the brightest galaxies, it has therefore not been listed in the famous catalog compiled by Charles Messier in the 18th century. The heart of the galaxy is composed of old stars that give this aspect reddish brown.
By cons, its spiral arms are home to younger stars, which give this their bluish color. With a size similar to our Milky Way, NGC 7331 is often seen as the apparent gathering of galaxies that can be seen in the background at the top of the image looks like a galaxy cluster.
However, they are not in the same cluster because they are located too far (several hundred million light years) of the galaxy NGC 7331. The image of the "universe island", an impressive depth of field was obtained from data collected from the earth's surface at the Calar Alto Observatory in southern Spain.


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

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

nota: IC (Index Catalogue of galaxies, nebulae and groups of Stars), serves as a supplement to the New General Catalogue.

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. 

Image: NGC 7331 tilted in our direction, we offer here the richness of its galactic environment. This image gives us a strikingly impression of depth amplified by the presence of distant galaxies. Credit & Copyright: Vicent Peris (OAUV / PTeam), Gilles Bergond, Calar Alto Observatory.

 Galaxie NGC 7331, Deer Lick group
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