Observing Hydra the Water Snake
The Largest Constellation in the Night Sky
The biggest of all 88 constellations wraps along the Milky Way low in the spring sky and contains three Messier objects.
Hydra the Water Snake is tied with the mythology of Crater the Cup and Corvus the Crow. Both Crater and Corvus are perched on the twisting form of the Water Snake. Hydra, largest of all the constellations, fills the space between the important zodiacal constellations along the ecliptic and the Milky Way.
Finding the Constellation Hydra
Hydra is located low in spring skies for observers in the Northern Hemisphere. The circlet that forms the head of the water snake lies below the constellation Cancer with its famous Beehive Cluster. The body extends away from the head toward the southeast. It runs below the forms of Sextans, Crater, Corvus, Virgo, and all the way to Libra.
Tracing the Form of Hydra
There are only a few stars of note in Hydra. The circlet marking the head of Hydra contains third and fourth magnitude stars. The brightest in the circlet is magnitude 3.11 Zeta Hydrae. Zeta Hydrae is sometimes considered part of the circlet and sometimes the first star that leads from the head to the body. This star lies 151 light-years away. Two degrees away is the next brightest star in this region of Hydra, Epsilon Hydrae at magnitude 3.38 lying 135 light-years away. The 4th magnitude star Rho Hydrae lies between these two, and three other 4th magnitude stars (Delta, Sigma, and Eta) complete the circlet.
The brightest star in Hydra lies about 16 degrees from the circlet. It is 23 degrees south of the bright star Regulus in Hydra. This is Alpha Librae, or Alphard, at magnitude 1.99. Alphard lies 177 light-years away.
Deep-Sky Objects in Hydra
There are three Messier objects in Hydra, an open cluster, a globular cluster, and a galaxy, in addition, a nice planetary nebulae is also found here, giving Hydra one good example of every deep-sky observing target.
M48 is an open cluster on the far western edge of Hydra. It lies 14 degrees from the bright star Procyon in Canis Minor. M48 is magnitude 5.8 and lies about 1,500 light-years away. This open cluster can be found without optical aid under dark skies but binoculars or a telescope will reveal about 50 of its 80 stars.
Hydra's planetary nebula is called the Ghost of Jupiter, or NGC 3242. This 9th magnitude nebula consists of a star at center with a bright nebula and then a ghostly cocoon around that. The entire size is about the apparent size of Jupiter. The Ghost of Jupiter can be found 31 degrees below the body of Leo the Lion.
The globular cluster in Hydra, M68, lies just three and a half degrees below the second brightest star in Corvus. M68 is magnitude 8.19 and lying 33,000 light-years away. It is a good sight through a telescope.
The last Messier object lies 13 degrees east from M68. M83 is a magnitude 7.6 barred spiral galaxy. Part of the Centaurus group of galaxies, M83 is one of the closer galaxies to Earth at a distance of 15 million light-years. It is sometimes referred to as the Southern Pinwheel Galaxy.
