Posted by on Mar 4, 2013 in Constellation Of the Month | 0 comments

Hydra (the constellation of the Water snake or Sea serpent) An original constellation. Mythologically it was a monster with a hundred heads. It was Hercules second labour to kill the monster, which he did. Hydra has the distinction of being the largest separate constellation in the Sky and also one of the dullest. Its has only one bright star, Alphard.

Star Visual Magnitude Spectrum Absolute Magnitude Distance (Lt Years)
Alphard 1.98 K4 -0.3 94
Y Hydra 2.98 G8 0.3 113
B Hydra 4.29 Ap Si -0.96 365


It is easy to find because a line drawn from Caster through Pollux leads to it. Alphard has a strong orange colour. The head of Hydra lies near Cancer, and the huge snake winds its way below Leo, Covus and Virgo. While on the whole this is a rather sparse region of the sky containing primarily faint and distant galaxies, there are three Messier objects and several fine Herschel objects in the area, making the hunt worthwhile.

M-48 This is a fine open cluster over one half of a degree in diameter, and easily seen in binoculars. It is composed primarily of fairly bright stars, loosely concentrated to the centre. It is estimated to have about 75 stars in the area.

M-68 This rather bright globular cluster is about 8-10′ in diameter and is very compact, showing a bright, granulated core and many stars resolved around its edges.

M-83 This is one of the finest examples of a face on barred spiral galaxies in the sky. It is large, about 10′ in diameter, with an obvious central bar and spiral arms which seem to go all the way around the galaxy. Often photographed by amateurs, this is a real gem of the night sky.

NGC 3242 This is a very impressive planetary nebula, discovered in 1785 by William Herschel. Showing a blue-green disk almost 1′ in diameter with a bright centre and fuzzy edges. There is a bright spot on the southeast edge, and another but fainter brightening to its northwest. This planetary nebula is most frequently called the Ghost of Jupiter or Jupiter’s Ghost, but it is also sometimes referred to as the Eye nebula. It can easily be observed with amateur telescopes, and appears bluish-green to most observers. Larger telescopes can distinguish the outer halo as well.