Hydra
The longest constellation in the whole sky
Best on March–May evenings · southern sky.
Hydra, the Water Snake, is the largest constellation by area — a long, winding river of stars that stretches nearly a third of the way around the sky. It slithers across the southern celestial hemisphere, threading between more compact constellations and taking a patient sweep of the eyes to trace from head to tail. Despite its size it has just one truly bright star, making Alphard all the more striking for its isolation.
How to find it
Spring evenings are the time to look, when Hydra sprawls across the southern sky for northern observers and rides high for those in the southern hemisphere. Start at Leo: find bright Regulus, then slide south and west to pick out a small tight knot of stars — that's the Water Snake's head. From there, follow the faint chain of stars eastward, curving gently south, until it ends far across the sky beneath Virgo.
Brightest stars
Alphard, the alpha star, shines alone at magnitude 1.98 with a warm orange glow — its name literally means 'the solitary one,' and it earns that title with nothing bright nearby. The next named stars, Hydrobius at magnitude 3.11 and Minchir at 4.44, are considerably fainter and lie along the snake's winding body.
Worth seeing
Alphard itself is the reward — a solitary orange beacon with no bright neighbors to distract the eye, glowing warmly against a relatively empty stretch of sky and marking the heart of the great serpent.
Frequently asked
When is Hydra visible?
Spring evenings, roughly March through May, when it stretches across the southern sky. Northern hemisphere observers see it low in the south; southern hemisphere observers get a better, higher view.
What are the brightest stars in Hydra?
Alphard (magnitude 1.98) is by far the brightest — an orange giant sitting in lonely splendor. Hydrobius follows at magnitude 3.11, and Minchir at 4.44 are the only other named stars in the constellation.
Which hemisphere is Hydra best seen from?
Hydra sits in the southern celestial hemisphere and is best seen from the southern hemisphere, though its western end including Alphard is easily visible from mid-northern latitudes on spring evenings.
Nearby constellations
Corvus · Leo · Puppis · Virgo · Cancer · Centaurus · Crux · Carina