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Corvus, a Constellation for May

Contributed by Paul Rodmell, Southland Astronomical Society

CORVUS, the Crow   (Pronounced Kor-vus)

Chart showing the constellation.

Corvus, the Crow, is a small constellation of ancient origin, to which Ptolemy assigned seven stars. It can be recognised by four prominent stars in a trapezium shape. The fifth star α Corvi is so much less bright than the others that it may have decreased in light since Bayer lettered them in 1603.

The ancient Greeks called this constelation "the Raven".

In legend, Corvus is associated with the neighbouring constellation of Crater, the Cup, and Hydra, the Water Snake. The crow is said to have been sent by Apollo to gather water in a cup, but instead it dallied to eat figs. When the crow returned to Apollo, it carried the water snake in its claws, claiming this creature to have been the cause of the delay. Apollo, realising the lie, banished the trio to the sky, where the Crow and the Cup lie on the back of Hydra. For its misdeed the crow was condemned to suffer from eternal thirst, which is why crows croak so harshly.

In another legend, a snow-white crow brought Apollo the bad news that his lover Coronis had been unfaithful to him. In his anger, Apollo turned the crow black. Apollo and crows are closely linked in legend, for during the war waged by the giants with the gods, Apollo turned himself into a crow.

To find Corvus look north early evening and find the trapezium shape. (Use the bright star Spica in Virgo to aid orientation.)

Chart showing Corvus as seen high in the sky to the north at about 10 pm NZST in mid May.

Corvus and surrounding constellations

Constellation Crater Constellation Virgo Constellation Hydra

Details of some of the objects shown in the chart.

α Corvi, Al Chiba is a magnitude 4.0 white star 68 light years away.

β Crv, Kraz is a magnitude 2.7 yellow giant star 290 light years away.

γ Crv, Gienah is a magnitude 2.6 blue-white star 190 light years away.

δ Crv, Algorab is a wide double star 120 light years away. The brightest component visible to the unaided eye, is a magnitude 3.0 white star, that is accompanied by a magnitude 8.4 star often described as purplish in colour.

ε Crv, Minkar is a magnitude 3.0 red star, about 300 light years away and 450 times as luminous as the Sun.

NGC 4038 and NGC 4039 are called the Antennae or Rat tailed or Ring-tailed galaxies. They are two galaxies in collision, and photographs show two tails of stars ejected from the interaction. The system is a strong radio transmitter. At magnitude 10.5 a reasonable telescope and dark skies are needed to see this. The rat tails are not visible in telescopes.

NGC 4782 and NGC 4783 are also two small elliptical galaxies in contact. The similar components with bright centres, appear in a field sprinkled thinly with faint stars. Photographs show diffuse material connecting the galaxies. At magnitude 11.7 a reasonable telescope and dark skies are needed for viewing these galaxies.

NGC 4361 is a planetary nebula with a visible central star. Only the central star can be seen in small telescopes, but larger telescopes will show the haze surrounding the star. An OIII filter effects a small improvement.

Just over the border of Corvus in the constellation Virgo lies the famous Sombrero galaxy, M 104. It is a spiral galaxy with a large nucleus and a dense lane of dust lying about 35 million light years away.

Visibility

Corvus is due north and high in the sky soon after 9 pm in mid May. It remains visible for at least part of the evening until about mid September when it will ve low, to the west-south-west as the sky darkens following sunset.



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