Canis Minor Constellation

Canis Minor Constellation.

Canis Minor is a small constellation in the northern celestial hemisphere. In the second century, it was included as an asterism, or pattern, of two stars in Ptolemy’s 48 constellations, and it is counted among the 88 modern constellations. Its name is Latin for “lesser dog,” in contrast to Canis Major, the “greater dog;” both figures are commonly represented as following the constellation of Orion, the hunter. The constellation boundaries, as set by Eugène Delporte in 1930, are defined by a polygon of 14 sides. Lying directly south of Gemini’s bright stars Castor and Pollux, Canis Minor is bordered by Monoceros to the south, Gemini to the north, Cancer to the northeast, and Hydra to the east. It does not border Canis Major; Monoceros is in between the two. Covering 183 square degrees, it ranks seventy-first of the 88 constellations in size. It appears prominently in the southern sky during the Northern Hemisphere’s winter. In the equatorial coordinate system, the right ascension coordinates of these borders lie between 07^h 06.4^m and 08^h 11.4^m, while the declination coordinates are between 13.22° and −0.36°. Most visible in the evening sky from January to March, Canis Minor is most prominent at 10 PM during mid-February. It is then seen earlier in the evening until July when it is only visible after sunset before setting itself, and rising in the morning sky before dawn.

Canis Minor contains only two stars brighter than fourth magnitude. At magnitude 0.34, Procyon, or Alpha Canis Minoris, is the seventh-brightest star in the night sky, as well as one of the closest. Its name means “before the dog” or “preceding the dog” in Greek, as it rises an hour before the “Dog Star,” Sirius, of Canis Major. It is a binary star system, consisting of a yellow-white main sequence star of spectral type F5 IV-V, named Procyon A, and a faint white dwarf companion of spectral type DA named Procyon B. Procyon B, which orbits the more massive star every 41 years, is of magnitude 10.7. Procyon A is 1.4 times the Sun’s mass, while its smaller companion is 0.6 times as massive as the Sun. The system is 11.4 light-years from Earth. Gomeisa, or Beta Canis Minoris, with a magnitude of 2.89, is the second-brightest star in Canis Minor. Lying 162 light-years from the Solar System, it is a blue-white main sequence star of spectral class B8 Ve. Although fainter to Earth observers, it is much brighter than Procyon and is 250 times as luminous and three times as massive as the Sun. Although its variations are slight, Gomeisa is classified as a shell star (Gamma Cassiopeiae variable), with a maximum magnitude of 2.84 and a minimum magnitude of 2.92. It is surrounded by a disk of gas which it heats and causes to emit radiation.

The Milky Way passes through much of Canis Minor, yet it has a few deep-sky objects. William Herschel recorded four objects in his 1786 work Catalogue of Nebulae and Clusters of Stars, including two he mistakenly believed were star clusters. NGC 2459 is a group of five thirteenth- and fourteenth-magnitude stars that appear to lie close together in the sky but are not related. A similar situation has occurred with NGC 2394, a collection of fifteen unrelated stars of ninth-magnitude and fainter. Herschel also observed three faint galaxies, two of which are interacting with each other. NGC 2508 is a lenticular galaxy of thirteenth-magnitude, estimated at 205 million light-years distance with a diameter of 80 thousand light-years. Named as a single object by Herschel, NGC 2402 is a pair of near-adjacent galaxies that appear to be interacting with each other. Only of fourteenth- and fifteenth-magnitudes respectively, the elliptical and spiral galaxy is thought to be approximately 245 million light-years distant, and each measure 55,000 light-years in diameter.

The 11 Canis-Minorids, also called the Beta Canis Minorids, are a meteor shower that arises near the fifth-magnitude star 11 Canis Minoris and was discovered in 1964 by Keith Hindley. They last from 4 to 15 December, peaking over 10 and 11 December. Credit: Wikipedia.