THE GALAXY

                                                                                                                                                           THE GALAXY                                                                                                                                                                                                                                                                                                           A galaxy is a gravitationally bound system consisting of stars, stellar remnants, an interstellar medium of gas and dust, and dark matter. The word galaxy is

derived from the Greek galaxias  literally "milky", a reference to the Milky Way. Examples of galaxies range from dwarfs with just a few thousand (103) stars to giants with one hundred trillion (1014) stars each orbiting their galaxy's own center of mass. Galaxies have historically been categorized according to their visual morphology, including elliptical spiral, irregular and starburst. Many galaxies are believed to have black holes at their active center. The Milky Way's central black hole, known as Sagittarius has a mass four million times that of our Sun.

The word galaxy derives from the Greek term for our own galaxy, galaxias "milky one"), or kyklos galaktikos ("milky circle") due to its appearance as a "milky" band of light in the sky. In Greek mythology, Zeus places his son born by a mortal woman, the infant Heracles, on Hera's breast while she is asleep so that the baby will drink her divine milk and will thus become immortal. Hera wakes up while breastfeeding and then realizes she is nursing an unknown baby: she pushes the baby away and jet of her milk sprays the night sky, producing the faint band of light known as the Milky Way.In the astronomical literature, the capitalized word "Galaxy" is used to refer to our galaxy, the Milky Way, to distinguish it from the other galaxies in our universe. The English term Milky Way can be traced back to a story by Chaucer c. 1380:

When William Herschel constructed his catalog of deep sky objects in 1786, he used the term spiral nebula for certain objects such as M31. These would later be recognized as conglomerations of stars, when the true distance to these objects began to be appreciated, and they would later be termed island universes. However, the word Universe was understood to mean the entirety of existence, so this expression fell into disuse and the objects instead became known as galaxies.

Tens of thousands of galaxies have been catalogued, but only a few have been given a well-established name, such as the Andromeda Galaxy, the Magellanic clouds, the Whirlpool Galaxy and the Sombrero Galaxy. Astronomers work with numbers from certain catalogues, such as the Messier catalogue, the NGC (New General Catalogue), the IC (Index Catalogue), the CGCG (Catalogue of Galaxies and of Clusters of Galaxies), the MCG (Morphological Catalogue of Galaxies) and UGC (Uppsala General Catalogue of Galaxies). All of the well-known galaxies appear in one or more of these catalogues but each time under a different number. For example, the Messier 109, a spiral system which has the number 109 in the catalogue of Messier also codes NCG3992, UGC6937, CGCG 269-023, MCG +09-20-044 and PGC 37617.

Because it is customary in science to assign names to most of the studied objects, even to the smallest ones, the Belgian astrophysicist Gerard Bodifee and the classicist Michel Berger started a new catalogue (CNG-Catalogue of Named Galaxies) in which a thousand well-known galaxies are given meaningful, descriptive names in Latin (or Latinized Greek) in accordance with the binomial nomenclature that one uses in other sciences such as biology, anatomy, paleontology and in other fields of astronomy such as the geography of Mars. One of the arguments to do so is that these impressive objects deserve better than uninspired codes. For instance, Bodifee and Berger propose the informal, descriptive name Callimorphus Ursae Majoris for the well-formed barred galaxy Messier 109 in Ursa Major.