Hydra, the Water Snake, is the largest constellation in the sky, an ancient serpent of faint stars that crawls a long way across the spring sky.
At a glance
| stars in the figure | 21 |
|---|---|
| nearest star of the figure | Pi Hydrae, 101 light-years (31 pc) |
| farthest star of the figure | Eta Hydrae, 587 light-years (180 pc) |
| depth | the farthest is 5.8 × farther than the nearest |
Read off the piece’s own catalogue, the same values it draws with.
About Hydra
Hydra is one of the constellations catalogued by Ptolemy. It is often linked with the many-headed monster killed by Heracles, and also with the water snake of the story of Corvus and Crater, the crow and the cup that ride on its back. It is the largest constellation by area and so long that it takes hours to rise completely, its head below Cancer and its tail near Libra.
Most of its stars are faint. The exception is Alphard, whose Arabic name means the solitary one: an orange giant shining alone in an empty part of the sky. The snake’s head is a small, distinctive knot of stars, including Ashlesha and Minchir, south of Cancer.
Hydra holds the Ghost of Jupiter, a planetary nebula that looks like a pale planet in small telescopes, and the Southern Pinwheel, a bright spiral galaxy seen face-on. It is best seen on evenings in the northern spring, which is autumn in the south.
What you see in the piece
Flown out to, the serpent comes apart along its whole length: Pi Hydrae is the nearest of its stars and Eta Hydrae lies several times deeper. Its figure also borrows Alkes and Beta Crateris from the cup above it.
Questions
What is the largest constellation?
Hydra, the Water Snake. It covers more sky than any other constellation and stretches from below Cancer to near Libra.
What is the brightest star in Hydra?
Alphard, an orange giant whose name means the solitary one, because no other bright star lies near it.