The Carina Constellation

The Carina Constellation.

Carina is a constellation in the southern sky. Its name is Latin for the keel of a ship, and it was formerly part of the larger constellation of Argo Navis, the great ship of Jason and the Argonauts who searched for the Golden Fleece, until Nicolas Louis de Lacaille divided Argo into three sections in 1763, the other two being Puppis (the poop deck), and Vela (the sails of the ship). These three became established as separate constellations and were formally included in the list of 88 modern IAU constellations in 1930.

Carina contains Canopus, a white-hued supergiant that is the second brightest star in the night sky at magnitude −0.72, 313 light-years from Earth. Alpha Carinae, as Canopus is formally designated, is a variable star that varies by approximately 0.1 magnitudes. Its traditional name comes from the mythological Canopus, who was a navigator for Menelaus, king of Sparta. There are several other stars above magnitude 3 in Carina. Beta Carinae, traditionally called Miaplacidus, is a blue-white hued star of magnitude 1.7, 111 light-years from Earth. Epsilon Carinae is an orange-hued giant star similarly bright to Miaplacidus at magnitude 1.9; it is 630 light-years from Earth. Another fairly bright star is the blue-white hued Theta Carinae; it is a magnitude 2.7 star 440 light-years from Earth. Theta Carinae is also the most prominent member of the cluster IC 2602. Iota Carinae is a white-hued supergiant star of magnitude 2.2, 690 light-years from Earth.

Eta Carinae is the most prominent variable star in Carina; with a mass of approximately 100 solar masses and 4 million times as bright as the Sun. It was first discovered to be unusual in 1677, when its magnitude suddenly rose to 4, attracting the attention of Edmond Halley. Eta Carinae is inside NGC 3372, commonly called the Carina Nebula. It had a long outburst in 1827, when it brightened to magnitude 1, only fading to magnitude 1.5 in 1828. Its most prominent outburst made Eta Carinae the equal of Sirius; it brightened to magnitude −1.5 in 1843. However, since 1843, Eta Carinae has remained relatively placid, having a magnitude between 6.5 and 7.9. However, in 1998, it brightened again, though only to magnitude 5.0, a far less drastic outburst. Eta Carinae is a binary star, with a companion that has a period of 5.5 years; the two stars are surrounded by the Homunculus Nebula, which is composed of gas that was ejected in 1843.

Two asterisms are prominent in Carina. One is known as the ‘Diamond Cross,’ which is larger than the Southern Cross (but fainter), and, from the perspective of the southern hemisphere viewer, upside down, the long axes of the two crosses being close to parallel. Another asterism in the constellation is the False Cross, often mistaken for the Southern Cross, which is an asterism in Crux. The False Cross consists of two stars in Carina, Iota Carinae and Epsilon Carinae, and two stars in Vela, Kappa Velorum and Delta Velorum.

Carina is known for its namesake nebula, NGC 3372, discovered by French astronomer Nicolas Louis de Lacaille in 1751, which contains several nebulae. The Carina Nebula overall is an extended emission nebula approximately 8,000 light-years away and 300 light-years wide that includes vast star-forming regions. It has an overall magnitude of 8.0. Its central region is called the Keyhole, or the Keyhole Nebula. The Keyhole is about seven light-years wide and is composed mostly of ionised hydrogen, with two major star-forming regions. The Homunculus Nebula is a planetary nebula visible that is being ejected by the erratic luminous blue variable star Eta Carinae, the most massive visible star known.

Since the Milky Way runs through Carina, there are a large number of open clusters in the constellation, embedded in rich star fields. NGC 2516, an open cluster, is located 1100 light-years from Earth and has approximately 80 stars, the brightest of which is a red giant star of magnitude 5.2. NGC 3114 is another open cluster approximately of the same size, though it is more distant at 3000 light-years from Earth. The most prominent open cluster in Carina is IC 2602, also called the “Southern Pleiades.” It contains Theta Carinae and is a cluster of approximately 60 stars. The Southern Pleiades is particularly large for an open cluster, with a diameter of approximately one degree. NGC 3532 possesses approximately 150 stars that are arranged in an unusual shape, approximating an ellipse with a dark central area. Several prominent orange giants are among the cluster’s bright stars, of the 7th magnitude. Carina also contains the globular cluster NGC 2808.

One noted galaxy cluster is 1E 0657-56, the Bullet Cluster. At a distance of 4 billion light-years (redshift 0.296), this galaxy cluster is named for the shock wave seen in the intracluster medium, which resembles the shock wave of a supersonic bullet. The bow shock visible is thought to be due to the smaller galaxy cluster moving through the intracluster medium at a relative speed of 3000–4000 kilometres per second to the larger cluster. Because this gravitational interaction has been ongoing for hundreds of millions of years, the smaller cluster is being destroyed and will eventually merge with the larger cluster.

Carina contains the radiant of the Eta Carinids meteor shower, which peaks around January 21 each year.

Credit: Wikipedia.