Constellation, Female Water Snake
Hydra
The water snake, a long winding figure that stretches more than a quarter of the way around the sky. Its head lies south of Cancer, and its brightest star Alphard means the solitary one.
From New York on October 13, 2026, the centre of Hydra rises at 4:28 AM, is highest at 9:36 AM (34° above the horizon in the S) and sets at 2:48 PM.
In the 3D sky
The sky over New York turned towards Hydra. Drag to look around.
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Evening visibility over the year
Height of the constellation’s centre above the horizon at 10 pm local time on the 15th of each month, from New York. Above about 30° it is well placed.
Name and history
The Greeks linked this water snake with two stories. Most often it is the Lernaean Hydra, the many-headed monster that Heracles killed as one of his labours. Each time he struck off a head, two more grew back, until his charioteer Iolaus burned the stumps. In the sky it has only one head, perhaps the immortal one. In the other Greek story it is the water snake brought back by Apollo’s crow as an excuse for its delay, and Apollo set the snake, the crow and the cup in the sky together. Corvus and Crater still ride on its back.
Alphard comes from an Arabic phrase meaning the solitary one, because it shines alone in an empty stretch of sky. In Indian astronomy the snake’s head matches the lunar mansion Ashlesha, and in 2018 the IAU gave that name to the star Epsilon Hydrae. Chinese astronomers placed its stars within the Vermilion Bird of the South.
Sources: Ian Ridpath, Star Tales: Hydra, IAU Working Group on Star Names (WGSN): Modern IAU star names
Brightest stars
| Star | Designation | Magnitude | Distance |
|---|---|---|---|
| Alphard | α Hya | 1.99 | 180 light-years |
| Naja | γ Hya | 2.99 | 134 light-years |
| ζ Hya | ζ Hya | 3.11 | 167 light-years |
| ν Hya | ν Hya | 3.11 | 144 light-years |
| π Hya | π Hya | 3.25 | 101 light-years |
| Ashlesha | ε Hya | 3.38 | 129 light-years |
| ξ Hya | ξ Hya | 3.54 | 130 light-years |
| λ Hya | λ Hya | 3.61 | 113 light-years |
| μ Hya | μ Hya | 3.83 | 234 light-years |
| θ Hya | θ Hya | 3.89 | 114 light-years |
Facts
| Area | about 1,299 square degrees (1 of 88) |
|---|---|
| IAU abbreviation | Hya |
| Sky | Southern sky |
| Origin | Listed in Ptolemy’s Almagest, about AD 150, from older Greek tradition |
| Stars brighter than magnitude 5 | 44 |
| Centre (J2000) | 10.2 h, -15° |
Deep-sky objects
Galaxies, clusters and nebulae brighter than magnitude 9, from the OpenNGC catalogue. Most need binoculars or a telescope and a dark sky.
Boundaries: International Astronomical Union, via Astronomy Engine. Areas are computed from the boundaries by sampling (within about one percent). Names and lines: Stellarium. Stars: HYG Database. Deep-sky objects: OpenNGC. Calculated with Astronomy Engine, an open-source library verified against the US Naval Observatory and NASA JPL. Data sources
How to use this page
Choose your place and a night at the top. The answer and the 3D view show where the constellation is, when it is highest and whether it rises at all from where you are. The chart shows its stars and lines, and the tables list its brightest stars and the deep-sky objects inside it.
Frequently asked questions
When is a constellation best seen?
When it is highest in a dark sky, which the page gives for the night you pick. Each constellation is best placed in a particular season, because the stars rise about four minutes earlier every night.
Why can I not see a constellation from my place?
Constellations far south of the celestial equator never rise from northern places, and those far north never rise from southern ones. The page says when this is the case.
What are the constellation boundaries?
The International Astronomical Union divides the sky into 88 areas with official boundaries. The stick figures are only a drawing aid, the boundaries say which constellation a point in the sky belongs to.
Related guides
- How to learn the constellationsStart with one bright pattern you cannot miss, use it as a signpost to its neighbours, and come back a month later: the sky will have turned, and you will know a little more of it.
- Altitude and azimuth: finding things in the skyTwo angles tell you exactly where to look: which direction, and how high.
- Light pollution and dark skies: the Bortle scaleFrom a city centre you can count a few dozen stars. From a truly dark site you can count a few thousand, with the Milky Way bright enough to cast a shadow. The Bortle scale puts a number on the difference.
- Binoculars for stargazing: what to buy and what to look atA pair of 7x50 or 10x50 binoculars shows the craters of the Moon, the moons of Jupiter, dozens of star clusters and the Andromeda Galaxy, for a fraction of the cost of a telescope.