Hydra is the largest constellation in the sky, but it contains only a few prominent stars. It stretches and zig-zags across more than a quarter of the celestial sphere. Some of its stars are relatively bright, but they are so scattered that they are hard to distinguish as a single constellation. Hydra is best seen from February to May.
History and Mythology
Hydra is associated with the myth of Corvus. In ancient days, Corvus, Crater, and Hydra were one constellation that formed a monster in the sky. Hydra is the snake that Corvus blamed for detaining him on his mission to take water to Apollo. It has also been identified as the many-headed monster killed by Hercules as his second labor.
Notable Starss
Alpha Hydrae or Alphard, meaning "the solitary one" in Arabic, is an orange giant of second magnitude that is over 175 light-years away. It is seen as the heart of the snake.
Beta Hydrae is a 4th magnitude double star with a separation of only 0.9 arcseconds.
Clusters, Nebulae, and Galaxies
M 48 is a 6th magnitude open cluster located on the western border of Hydra. At a distance of about 1,500 light-years, it is barely visible with the naked eye. A small telescope reveals about 80 stars in the cluster.
Messier 68 is an 8th-magnitude globular cluster quite difficult for Northern observers to see because of its southern declination. Appearing as faint patch in binoculars, M 68 lies at a distance of about 33,000 light years. NGC 5694 is an extremely distant globular cluster in the constellation Hydra, 113,200 light years from the Sun, and appears to be moving so fast that it is destined to escape from our Galaxy into intergalactic space.
The planetary nebula NGC 3242 is sometimes called the "ghost of Jupiter" because it resembles the disk of Jupiter. In a small telescope it appears as a 9th magnitude blue-green oval. In larger instruments it shows as a bright inner disk surrounded by a fainter halo.
M 83 is a large, face on spiral galaxy that is visible in small telescopes, and is one of the brightest galaxies in the southern sky. In larger instruments, two spiral arms can be seen extending outward from the nucleus. M 83 is known to have produced an unusual number of supernovae - at least six since the start of the 20th century!