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Hydra
The Water Snake
Hydra - Celestial Atlas by Alexander Jamieson - 1822
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Hydra is the largest and longest constellation in the sky. It stretches fully one quarter of the way around the horizon, and takes up two full pages of Alexander Jamieson's 1822 Celestial Atlas. Although the celestial Hydra has only one head, its mythological namesake apparently had many, as well as poisonous breath and blood. It guarded one of the entrances to the underworld, and the killing of this fearsome creature was the second of the twelve labours of Hercules. At first Hercules had trouble dealing with the monster, because every time he chopped off its head, two more would grow in its place. Hercules finally discovered that burning the stump of a severed head would stop it from growing another one, and he was able to defeat the monster. The gods placed it in the sky to commemorate his victory.
The alpha star in the constellation Hydra is Alphard, which means the solitary one, because it is the only bright star in that region of the sky. It is also known as Cor Hydrae, the heart of the Hydra. It is 95 light years away.
M83 (NGC 5236) is one of the closest and brightest spiral galaxies in the southern sky. It is only 10 million light years away, and with an apparent magnitude of 7.54, almost visible with the naked eye. Like our Milky Way, it is a barred spiral galaxy, but with a diameter of only 40,000 light years, it's less than half the size of our galaxy.
With an apparent magnitude of 9.67, M68 is not one of the brighter globular clusters, but still visible in a small scope. It is 33,000 light years away.
NGC 3314, with a magnitude of 12.5, is only visible in very large telescopes. It is actually two overlapping galaxies, and although they appear to be colliding, they are actually very far apart. NGC 3314a is about 117 million light years away, and NGC 3314b, in a direct line of sight behind it, is about 140 million light years away.
M48 (NGC 2548) is an open star cluster at the very edge of the constellation's western border. NGC 3242 is a planetary nebula often called the ghost of Jupiter, and is a fine sight in a small telescope. Located near the tail of the Hydra, is the globular cluster NGC 5694. It is over 100,000 light years away.
No less than 14 planets have been discovered so far in the constellation Hydra. One of these planets orbits a star visible (just barely) with the naked eye. The star is HD 122430, near the tail of the snake. For more information, go to NASA's Planet Quest.
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