Carina

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Carina

The stellar southern constellation Carina is part of the Milky Way and is part of the old constellation of Argo Navis. It is now abbreviated and represents the “Keel”. It consists of 9 primary stars and has 52 Bayer/Flamsteed designated stars. Carina is bordered by Vela, Puppis, Pictor, Volans, Chamaeleon, Musca and Centaurus. It is visible at latitudes between +20° and ?90° and is best seen during the month of March.

While Carina has no real mythology associate with it since it wasn’t visible to the ancient Greeks and Romans, it does have some very lovely tales and a fascinating history. Argo Navis (or simply Argo) was a large southern constellation representing the Argo, the ship used by Jason and the Argonauts in Greek mythology. The Argo was built by the shipwright Argus, and its crew were specially protected by the goddess Hera. The best source for the myth is the Argonautica by Apollonius Rhodius. According to a variety of sources of the legend, the Argo was said to have been planned or constructed with the help of Athena. According to other legends it contained in its prow a magical piece of timber from the sacred forest of Dodona, which could speak and render prophecies. After the successful journey, the Argo was consecrated to Poseidon in the Isthmus of Corinth. It was then translated into the sky and turned into the constellation of Argo Navis.

The abbreviation was “Arg” and the genitive was “Argus Navis”. It is the only one of Ptolemy’s list of 48 constellations that is no longer officially recognised as a constellation. French astronomer Nicolas Louis de Lacaille in 1752 subdivided Argo Navis into Carina (the keel of the ship), Puppis (the Poop deck), and Vela (the sails). Were this still considered to be a single constellation, it would be the largest of all, being larger than Hydra. When Argo Navis was split, its Bayer designations were also split. Carina has the Alpha, Beta and Epsilon, Vela has Gamma and Delta, Puppis has Zeta, and so on. The constellation Pyxis occupies an area which in antiquity was considered part of Argo’s mast. However, Pyxis is not now (usually) considered part of Argo Navis, and in particular its Bayer designations are separate from those of Carina, Puppis and Vela.

Before you even begin with a telescope or binoculars, be sure to stop and just take a good look at Alpha Carinae – Canopus. Not only is Canopus the brightest star constellation of Carina, but it’s the second brightest star in the night-time sky, after Sirius. Canopus’s visual magnitude is ?0.72, and it has an absolute magnitude of ?5.53. What’s more, Canopus is a rare example of a supergiant of spectral type F. Canopus is essentially white when seen with the naked eye (though F-type stars are sometimes listed as “yellowish-white”). Before the launching of the Hipparcos satellite telescope, distance estimates for the star varied widely, from 96 light years to 1200 light years. Had the latter distance been correct, Canopus would have been one of the most powerful stars in our galaxy. Hipparcos established Canopus as lying 310 light years (96 parsecs) from our solar system; this is based on a parallax measurement of 10.43 ± 0.53 mas. The difficulty in measuring Canopus’ distance stemmed from its unusual nature. The spectral classification for Canopus is F0 Ia (Ia referring to “bright supergiant”), and such stars are rare and poorly understood; they are stars that can be either in the process of evolving to or away from red giant status. This in turn made it difficult to know how intrinsically bright Canopus is, and therefore how far away it might be. Direct measurement was the only way to solve the problem. Canopus is too far away for Earth-based parallax observations to be made, so the star’s distance was not known with certainty until the early 1990s. Canopus is 15,000 times more luminous than the Sun and the most intrinsically bright star within approximately 700 light years. For most stars in the local stellar neighborhood, Canopus would appear to be one of the brightest stars in the sky. Canopus is out-shone by Sirius in our sky only because Sirius is far closer to the Earth (8 light years). Its surface temperature has been estimated at 7350 ± 30 K. and its stellar diameter has been measured at 0.6 astronomical units 65 times that of the sun. If it were placed at the centre of the solar system, it would extend three-quarters of the way to Mercury. An Earth-like planet would have to lie three times the distance of Pluto! Canopus is part of the Scorpius-Centaurus Association, a group of stars which share similar origins.

Since the Milky Way runs through Carina, there are a large number of open clusters in the constellation making it a binocular observing paradise. NGC 2516 is a magnitude 3.1 open cluster originally discovered by Abbe Lacaille in 1751 with a 1/2″ spyglass. This gorgeous 30 arc minute spread of stars is also known as Caldwell 96 and graces many observing lists, including the Astronomical League Open Cluster, Deep Sky and Southern Observing Clubs. It is commonly known as the “Southern Beehive Cluster” (for it does resemble northern Messier 44) and it contains about 100 stars the brightest of which is an fifth magnitude red giant that lies near the center. As far as stellar age goes, this star cluster is very young… only about 140 million years old!

Now hop to IC 2602, popularly known as the “Southern Pleiades” for is resembalance to northern Messier 45. This galactic cluster contains more than 50 stars and is approximately 500 light years away from Earth. At its heart is blue-white star Theta Carinae, and it can be found by forming a triangle in the sky with Beta and Iota Carinae. With a stellar magnitude of 2.0, this object is easily seen as a nebulous patch to the unaided eye!

Another nebula that can been seen unaided but is better in binoculars is the Homunculus in NGC 3372, best known as the Eta Carinae Nebula. The Homunculus Nebula is part of an emission nebula surrounding the massive star Eta Carinae. The nebula is embedded within a much larger H II region, the Eta Carinae Nebula. The Homunculus (which is from the Latin meaning Little Man) is believed to have been ejected in an enormous outburst which Eta Carinae underwent, the light of which first reached Earth in 1841. Following this outburst, Eta Carinae became the second-brightest star in the sky after Sirius, but since this time, the gas and dust it ejected has obscured much of its light. The explosion produced two polar lobes and a large thin equatorial disk, all moving outward at about 1.5 million miles per hour. Future eruptions are still a possibility.

Even though Eta Carinae is about 7,500 light-years away, structures only 10 billion miles across (about the diameter of our solar system) can be distinguished. Dust lanes, tiny condensations, and strange radial streaks all appear with unprecedented clarity. The outer ejecta blobs are 100,000 times fainter than the brilliant central star. Excess violet light escapes along the equatorial plane between the bipolar lobes. Apparently there is relatively little dusty debris between the lobes down by the star; most of the blue light is able to escape. The lobes, on the other hand, contain large amounts of dust which preferentially absorb blue light, causing the lobes to appear reddish.

The Eta Carinae Nebula, or NGC 3372 is a large bright planetary nebula that surrounds several open clusters of stars. Eta Carinae and HD 93129A, two of the most massive and luminous stars in our Milky Way galaxy, are among them. The nebula lies at an estimated distance between 6,500 and 10,000 light years from Earth. It is located in the constellation of Carina. The nebula contains multiple O-type stars. This nebula is one of the largest H II regions in the Milky Way. It has a visual magnitude of 1.0. The nebula is one of the largest diffuse nebulae in our skies. Although it is some four times as large and even brighter than the famous Orion Nebula, the Carina Nebula is much less well known, due to its location far in the Southern Hemisphere.

Eta Carinae itself is fascinating. It is a hypergiant luminous blue variable star in the Carina constellation. Its luminosity is about four million times that of the Sun and, with an estimated mass of between 100 and 150 solar masses, it is one of the most massive stars yet discovered. Because of its mass and the stage of life, it is expected to explode in a supernova in the “near” future. This object is currently the most massive nearby star that can be studied in great detail. While it is possible that other known stars might be more luminous and more massive, Eta Carinae has the highest confirmed luminosity based on data across a broad range of wavelengths; former prospective rivals such as the Pistol Star have been demoted by improved data. Stars in the stellar mass class of Eta Carinae, with more than 100 times the mass of the Sun, produce more than a million times as much light as the Sun. They are quite rare — only a few dozen in a galaxy as big as the Milky Way. They are assumed to approach (or potentially exceed) the Eddington limit, i.e., the outward pressure of their radiation is almost strong enough to counteract gravity. Stars that are more than 120 solar masses exceed the theoretical Eddington limit, and their gravity is barely strong enough to hold in their radiation and gas.

Now hop just three degrees away to NGC 3532 – known as the “Wishing Well Cluster”. This open star cluster is one of the jewels of the southern sky and so named because its stars look like coins shimmering at the bottom of a Wishing Well. It is also referred to as Caldwell 91 and is on many observing lists! Another? Try globular cluster NGC 2808, also known as Bennett 41. Beautiful NGC 2808 is a fine example of a symmetrical and strongly compressed globular cluster. Viewable in binoculars and totally resolvable in a 6″ telescope, this is another of Dreyer’s remarkable objects described as very large extremely rich, and gradually reaching an extremely condensed status in the middle. NGC 2808 contains thousands of magnitude 13-15 stars!

For double star fans, take on Epsilon Carinae, also known by the name Avior. Epsilon Carinae is a binary star located 630 light years away from our solar system. The primary component is a dying orange giant of spectral class K0 III, and the secondary is a hot hydrogen-fusing blue dwarf of class B2 V. The stars regularly eclipse each other, leading to brightness fluctuations on the order of 0.1 magnitudes. Now try Upsilon Carinae – part of the Diamond Cross asterism in southern Carina. It’s name is Vathorz Prior, a name of Old Norse-Latin origin meaning “Preceding One of the Waterline”. The Upsilon Carinae system has a combined apparent magnitude of +2.92 and is approximately 1623 light years from Earth. The primary component, Upsilon Carinae A, is a white A-type supergiant with an apparent magnitude of +3.01. The companion, Upsilon Carinae B, is a blue-white B-type giant with an apparent magnitude of +6.26. The two stars are 5 arc seconds apart.

But no constellation would be complete without a true telescope challenge. Planetary nebula NGC 3211 (RA 10h 17m 50.4s Dec -62° 40´ 12″) heralds in at about 12th magnitude. For even more fun, try NGC 2867 (R.A. 09h 21m 25.3s Dec. -58° 18′ 40.7″). You’ll find it about a degree north/northeast of Iota. Iota Carinae. NGC 2867 may be no more than 2,750 years old.1 It is unusual in being only one of a few dozen such objects known to have a Wolf-Rayet star (type WC6) as its central star. NGC 2867 was discovered by John Herschel from Felhausen observatory at the Cape of Good Hope on April Fools Day, 1834 – appropriately enough as Herschel was almost fooled into thinking it was a new planet. Its size and appearance were certainly planet-like and it was only after careful checking that Herschel was convinced it was a nebula.

Now try NGC 3247 (RA 10 : 25.9 Dec -57 : 56 ). This is a very cool, very small galactic cluster with associated nebulosity. At around magnitude 8, you won’t find the rich little cluster much of a problem, but use minimal magnifcation to appreciate the true field! While at the telescope, also look up NGC 3059 (9 : 50.2 Dec -73 : 55). Now, we’ve got a spiral galaxy cutting its way through the dust of the Milky Way! With an apparent magnitude of 12, and a 3.2 arc minute diameter, this barred spiral galaxy is going to present a nice, unique challenge to southern hemisphere observers.

There are myriad other things to look at in Carina as well, so don’t see this lovely constellation short! There is also a meteor shower associated with the constellation of Carina, too. The Eta Carinids are a lesser known meteor shower lasting from January 14 to 27 each year. The activity peaks on or about January 21. It was first discovered in 1961 in Australia. Roughly two to three meteors occur per hour at its maximum. It gets its name from the radiant which is close to the nebulous star Eta Carinae.

Source: Chandra Observatory
Constellation Chart Provided by Your Sky.

About Tammy Plotner

Tammy is a professional astronomy author, President Emeritus of Warren Rupp Observatory and retired Astronomical League Executive Secretary. She’s received a vast number of astronomy achievement and observing awards, including the Great Lakes Astronomy Achievement Award, RG Wright Service Award and the first woman astronomer to achieve Comet Hunter's Gold Status.