Hydra
What is Hydra?
Constellations· Spring evenings (N) · a serpent stretching over 100° from Cancer to Libra. The largest constellation in the sky, stretching a quarter of the way around from a small head below Cancer to a tail near Libra. Its only bright star is Alphard, "the solitary one". This is the nine-headed water snake Heracles slew.
📍 Visible from where you are right now — computed in your browser
bearing · altitude · rise time · best time tonight
Where Hydra is in your sky right now: https://nowsky.org/solar/sky?sel=con:Hydra — location and time set automatically, no login.
Stars of the figure
| Star | Magnitude |
|---|---|
| Alphard | 2.0 |
The 1 brightest of the 12 stars used in the figure (11 lines). Lower magnitude means brighter.
Deep-sky objects near this constellation
Constellation basics
| Season | spring evenings, March–May |
|---|---|
| Brightest star | Alphard (2.0) |
| How to find | from lonely Alphard southwest of Regulus, follow the faint line east |
| Area rank | 1st of 88 |
Figures are representative approximations. Source: compiled from NASA and IAU public data.
Frequently asked
- When can I see Hydra?
- spring evenings, March–May.
- How do I find Hydra?
- from lonely Alphard southwest of Regulus, follow the faint line east.
- What is the brightest star in Hydra?
- Alphard, magnitude 2.
- Where is Hydra in the sky right now?
- Open the sky view for your location and time and it shows the position in the sky right now.
The Southern Pinwheel — a galaxy where six supernovae have gone off
Deep in the southern sky toward the tail of Hydra lies M83, a spiral galaxy seen face-on. At 15 million light-years it is relatively near, and with its bar and clear arms it is called the Southern Pinwheel. Six supernovae have been observed in it since 1923, among the most recorded in any single galaxy — a galaxy where stars are born fast and die fast.
It was found by Lacaille from the Cape of Good Hope in 1752, one of the first galaxies beyond our own to enter a catalogue. From Seoul it rises barely 20° above the southern horizon, but in the southern hemisphere binoculars show it as a faint smudge. At the far end of the sky's largest constellation sits the galaxy where the deaths of stars come most often.
The constellation in depth
Hydra is the Lernaean water snake of Heracles' second labour: cut off one head and two grew back, until his nephew Iolaus seared each stump with fire while Hera sent a crab (Cancer) to hinder him. In another tale it is the snake the crow (Corvus) brought back to Apollo as an excuse for its lateness. The constellation was already enormous in Ptolemy's catalogue and has remained the largest of all 88 ever since the boundaries were fixed in 1930.
Alphard is Arabic for "the solitary one" — no bright star lies near it, so it shines alone in the spring sky. Five stars form a small loop at the head, and Corvus and Crater ride on the serpent's back. Within its borders are the Southern Pinwheel galaxy, M83, a fine spring target, and the planetary nebula called the Ghost of Jupiter, NGC 3242.
On spring evenings the lone star southwest of Regulus is Alphard. The small ring of stars to its northwest is the head, and faint stars run east beneath Corvus toward Libra. The figure is so long that the head sets before the tail has fully risen. Set the Sky view to an April night with the lines on to appreciate its full length.
Related
Figures are representative approximations. Simulated positions use J2000 mean elements.