The Capricornus Constellation.
Capricornus, as its name implies is Latin for “horned goat” or “goat horn”, and it is commonly represented in the form of a sea-goat: a mythical creature that is half goat, half fish. Capricornus is one of the 88 modern constellations and was also one of the 48 constellations listed by the 2nd-century astronomer Ptolemy. Under its modern boundaries, it is bordered by Aquila, Sagittarius, Microscopium, Piscis Austrinus, and Aquarius. The constellation is located in an area of sky called the Sea or the Water, consisting of many water-related constellations such as Aquarius, Pisces, and Eridanus. It is the smallest constellation in the zodiac. The best viewing month is September at Right Ascension 21h 3m, Declination -19degrees 21’.
Capricornus is a faint constellation, with only one star above magnitude 3; its alpha star has a magnitude of only 3.6. The brightest star is δ Capricorni, also called Deneb Algedi, with a magnitude of 2.9, 39 light-years from Earth. Like several other stars such as Denebola and Deneb, it is named for the Arabic word for “tail” (deneb); its traditional name means “the tail of the goat.” Deneb Algedi is a Beta Lyrae variable star. The other bright stars in Capricornus range in magnitude from 3.1 to 5.1. α Capricorn is a multiple star also known as Algedi or Giedi. The primary (α2 Cap), 109 light-years from Earth, is a yellow-hued giant star of magnitude 3.6.; the secondary (α1Cap), 690 light-years from Earth, is a yellow-hued supergiant star of magnitude 4.3. Both are themselves multiple stars: α1 Capricorni is accompanied by a star of magnitude 9.2; α2 Capricornus is accompanied by a star of magnitude 11.0; this faint star is itself a binary star with two components of magnitude 11. β Capricorni is a double star also known as Dabih. It is a yellow-hued giant star of magnitude 3.1, 340 light-years from Earth. The secondary is a blue-white hued star of magnitude 6.1.
Several galaxies and star clusters are contained within Capricornus. Messier 30 is a globular cluster located 1 degree south of the galaxy group NGC 7103. The constellation also harbours the wide spiral galaxy NGC 6907. M30 (NGC 7099) is a centrally-condensed globular cluster of magnitude 7.5 at a distance of 30,000 light-years. One galaxy group located in Capricornus is HCG 87, a group of at least three galaxies located 400 million light-years from Earth (redshift 0.0296). It contains a large elliptical galaxy, a face-on spiral galaxy, and an edge-on spiral galaxy. The face-on spiral galaxy is experiencing abnormally high rates of star formation, indicating that it is interacting with one or both members of the group. Furthermore, the large elliptical galaxy and the edge-on spiral galaxy, both of which have active nuclei, are connected by a stream of stars and dust, indicating that they too are interacting. Astronomers predict that the three galaxies may merge millions of years in the future to form a giant elliptical galaxy.
Credit: Go Astronomy, Wikipedia.