What it looks like
Hydra is the largest of the 88 constellations, winding across the southern celestial hemisphere from near Cancer in the west to Libra in the east. It is drawn as a water snake, with Alphard — its only bright star — marking the heart. Its great length makes it fully visible only on spring evenings from mid-northern latitudes.
Brightest stars
Hydra has one clearly bright star, Alphard, plus a long tail of fainter stars winding eastward.
| Star | Magnitude | Distance | Meaning |
|---|---|---|---|
| Alphard (α Hydrae) | +1.98 | 177 ly | The Solitary One |
| Gamma Hydrae | +2.99 | 134 ly | — |
| Nu Hydrae | +3.11 | 138 ly | — |
| Zeta Hydrae | +3.11 | 151 ly | — |
| Pi Hydrae | +3.25 | 101 ly | — |
Mythology and history
In Greek myth, Hydra is the Lernaean Hydra, a many-headed serpent slain by Heracles as his second labour.
The Lernaean Hydra
The Hydra was a monstrous water serpent with many heads, living in the swamps of Lerna. Every time Heracles cut off one head, two more grew in its place. With the help of his nephew Iolaus, who cauterised each stump with a burning brand, Heracles finally killed it, then dipped his arrows in its poisonous blood. The constellation was placed in the sky by Hera, who had raised the Hydra to test Heracles. Because it is so long, it takes more than six hours to fully rise above the horizon.
How to find it
Look for a long, faint chain of stars running from below Cancer eastward toward Libra on spring evenings, with Alphard as the brightest link.
- Find Alphard below Leo, then trace the snake eastward.
- Hydra is so long that part of it is always above the horizon on spring evenings.
- Best on spring evenings from the northern hemisphere.
Key facts
- Abbreviation
- Hya
- Genitive
- Hydrae
- Meaning
- The Water Snake
- Brightest star
- Alphard
- Main stars
- 17
- Area rank
- 1st
- Best visible
- April
- Declination
- -20°
- Meteor showers
- Alpha Hydrids, Sigma Hydrids
- Neighbours
- Antlia, Cancer, Canis Minor, Centaurus, Corvus, Crater, Leo, Libra, Lupus, Monoceros, Puppis, Pyxis, Sextans, Virgo
Deep-sky objects
Hydra contains three Messier objects: M48, M68 and M83 (the Southern Pinwheel Galaxy). The constellation also hosts the Hydra Cluster of galaxies and the planetary nebula NGC 3242, known as the Ghost of Jupiter.
Frequently asked questions
What does the constellation Hydra look like?
Hydra is the largest constellation in the sky, known as the Water Snake, stretching over 100 degrees from Cancer to Libra with the bright star Alphard marking its heart.
What is the brightest star in Hydra?
The brightest star in Hydra is Alphard, shining at around magnitude 1.98.
When is Hydra best visible?
Hydra is best seen from both hemispheres during April.
What is the story behind Hydra?
In Greek myth, Hydra is the Lernaean Hydra, a many-headed serpent slain by Heracles as his second labour.
Which constellations are near Hydra?
Hydra borders Antlia, Cancer, Canis Minor, Centaurus, Corvus, Crater, Leo, Libra, Lupus, Monoceros, Puppis, Pyxis, Sextans and Virgo.
Leo
Libra