Carina

Carina


Transit Date of principal star:
27 December


When the twins Castor and Pollux went off with Jason and the rest of the Argonauts, they sailed in the Argo, a ship built by Argus. This ship, equipt with fifty oars and manned by fifty of the best men of Greece, sailed to Colchis, which was at the eastern shore of the Black Sea.

After many adventures Jason (with Medea's help) stole the fleece from the dragon and they all sailed back home.

Athene is said to have commemorated the event by placing their ship, Argo Navis, in the sky as a giant constellation below and east of Canis Major. What is known is that Edmund Halley's catalogue of the southern stars, Catalogus stellarum australium (1679), introduced Argo Navis to the world.

In 1763 Nicolas Louis de Lacaille's posthumous work Caelum australe stelliferum gave us most of the constellations we now know in the southern hemisphere. Lacaille divided the gigantic Argo Navis into three constellations: Carina (the Keel), Puppis (the Stern, or Poop deck), and Vela (the Sail). To this day the Bayer letters (Greek letters) are divided among these three. By far the most interesting of these three is Carina.


Carina is home to Canopus (alpha Carinae), the second brightest star in the heavens.
Its name is said to come from the pilot of the fleet of ships of King Menelaus. It was this king of Sparta who rallied the men of Sparta to fight for Helen of Troy; his prize was Helen herself, who became his queen. Of Canopus, the pilot, it is said that he died in Egypt after the fall of Troy.

Canopus -- the star -- was known in antiquity as the Star of Osiris and worshipped in many ancient cultures. This was the star that Posidonius used in Alexandria, circa 260 BC, as he became the first person to plot out a degree of the Earth's surface.

While the brightest star in the southern hemisphere, Canopus is not visible to anyone living above latitude 30 degrees north. Thus Europe north of Lisbon cannot see the star, and for North America the star is visible only for those living south of a line drawn between San Francisco and Washington D.C., depending on local topography of course.

For inhabitants of the southern hemisphere, Canopus announces the beginning of summer, for it culminates on December 27.

Canopus is a supergiant around thirty-five times the diameter of the Sun. Prior to the Hipparcos satellite, the distance of Canopus was difficult to calculate, with estimates ranging from 160 to over 1200 light years. Hipparcos has calculated the distance at 313 light years (96 parsecs). The star has a luminosity of over 12,000.


As pointed out above, there are only a few Bayer stars, as this constellation is only part of an originally much larger one.

The most interesting object of the constellation is Eta Carinae: a mystery star which changes its magnitude very irregularly, from a brilliant -0.8 in 1843 to a rather dim -7 in the mid 1870s. Its present visual magnitude isn't much brighter, at only 6.21.

The star's absolute magnitude has been difficult to assess. If we take the distance to be 2000 parsecs, as some authorities would have it, then we arrive at an absolute magnitude of -5.3 (and a distance of 6500 light years). On the other hand Burnham gave an absolute magnitude of -3.3, and a distance of 2600 light years.

The star is considered to be either a very young one, not yet on the main sequence, or a very old one, approaching its eventual demise. At the present time the latter view seems prevalent. When it finally does die, it might create one of the brightest supernovae ever seen.

Eta Carinae is associated with the Keyhole Nebula (see below)


Double stars in Carina:

Upsilon Carinae is easily resolved, a pleasant binary of two white stars (visual magnitudes 3.0, 6.0), 127 and separation of 5.0".

Variable stars:

Chi Carinae is a cepheid variable, from 3.46 to 3.475 every two hours and twenty-five minutes.

R Carinae is a Mira-type red giant ranging from 3.9 to 10.5 every 308.71 days.

ZZ Carinae ("el") is an unusual cepheid with variations that are quite noticeable to the naked eye. From its maximum of 3.3 it slowly dims over a three-week period to about 4.0, then it takes only seven days to achieve its brightest again, before the slide begins all over again.


Deep Sky Objects:

NGC 2516. A very nice open cluster of perhaps a hundred stars, located fifteen degrees SE of Canopus. with a red giant at the centre. It's estimated at 1200 light years away.

NGC 3372, The Keyhole Nebula. A diffuse nebula of great complexity and beauty. While the nebula is composed of brightly glowing gas, there are darker areas which serve to break the nebula into individual islands. The most dramatic of these darker areas has been labelled the Keyhole because of its shape. Eta Carina is found in this nebula.

NGC 3532. A spectacular cluster of four hundred or so mostly bright, sparkling white, class A stars. John Herschel thought this was the finest cluster he'd ever seen. It's located three degrees WNW of eta Carinae.

IC 2602 is a group of thirty or so stars some 700 light years away; theta Carinae is the brightest member.


For a closer appreciation of Carina, visit the Binocular Section.


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