Hydra (the Water Snake) is the largest of the 88 constellations, stretching across more than 100 degrees of the night sky. Its long, winding outline extends beneath several familiar constellations, from Cancer in the west toward Libra in the east.
Despite covering an enormous area, Hydra has only one particularly bright star, Alphard, an orange giant traditionally associated with the heart of the snake. The constellation also contains three Messier objects, the Ghost of Jupiter planetary nebula, and several distant galaxies.
Where Is Hydra and When Can You See It?
Hydra covers approximately 1,303 square degrees, making it the largest constellation in the sky, occupying about 3.2% of the celestial sphere. It stretches across both celestial hemispheres, with its head lying below Cancer and its tail extending toward Libra and Centaurus.
The best time to observe Hydra is February through May, particularly April, when much of the constellation is visible during the evening. From mid-northern latitudes, including Britain, Hydra appears relatively low in the southern sky. Its great length means the entire constellation is not ideally positioned at once.
To find Hydra, begin below Cancer, where a small group of stars forms the snake’s head. From there, trace its winding body southeastward toward Alphard, the constellation’s brightest star, and onward beneath Leo and Virgo. Because Hydra’s stars are widely spread and mostly faint, identifying the full constellation is easier under dark skies.
Mythology of Hydra
In Greek mythology, Hydra is commonly associated with the Lernaean Hydra, a monstrous water serpent defeated by Heracles during the second of his famous labors.
The creature lived in a swamp near Lake Lerna and was said to possess numerous heads. Whenever Heracles cut off one head, two more grew in its place. To overcome the monster, Heracles enlisted the help of his nephew Iolaus, who used fire to cauterize each severed neck and prevent the heads from regenerating. During the battle, the goddess Hera sent a giant crab to distract Heracles. The crab was also defeated and later became associated with the constellation Cancer.
Another Greek tradition connects Hydra with a water snake carried by Apollo’s raven, represented by the neighboring constellations Corvus and Crater.
Notable Stars in Hydra
- Alphard (Alpha Hydrae) – The brightest star in Hydra, an orange giant approximately 177 light-years away, shining at magnitude 2.0. Its name comes from an Arabic expression meaning the solitary one, reflecting its isolated appearance in a relatively sparse region of sky. Alphard marks the heart of the Water Snake. Read more in our Alphard star guide.
- Gamma Hydrae – A yellow giant approximately 130 light-years away, with an apparent magnitude around 3.0. It is one of the brightest stars toward Hydra’s long eastern tail.
- Zeta Hydrae (Hydrobius) – An evolved yellow-white star approximately 150–170 light-years away, shining near magnitude 3.1. It lies in the western portion of the constellation, close to the snake’s head.
- Beta Hydrae – A multiple-star system approximately 370 light-years away, with a combined apparent magnitude around 4.3. Its primary is a chemically peculiar star whose brightness varies as it rotates.
- Gliese 433 – A faint red dwarf approximately 30 light-years away. Although invisible to the naked eye, it is of interest because astronomers have detected planets orbiting it.
Hydra also contains numerous fainter stars, but its size makes Alphard the most useful landmark for recognizing the constellation.
Notable Deep-Sky Objects in Hydra
Hydra contains three Messier objects — M48, M68, and M83 — along with several planetary nebulae, globular clusters, and distant galaxies.
Messier 48 — An Open Star Cluster
Messier 48 (M48, NGC 2548) is a large open cluster approximately 1,500 light-years away.
It contains dozens of bright stars spread across a broad area of sky and has an apparent magnitude around 5.5.
Under dark conditions, M48 can be glimpsed without optical equipment, while binoculars provide an attractive view of its loosely arranged stars.
It is one of Hydra’s most accessible deep-sky targets for beginners.
Messier 68 — A Globular Cluster
Messier 68 (M68, NGC 4590) is a globular cluster approximately 33,000 light-years away, shining at an apparent magnitude around 7.8.
It contains a large population of old stars held together by gravity and appears as a faint, rounded glow through small telescopes.
Larger instruments begin to resolve individual stars toward its outer regions, although its relatively low position in the sky makes it a challenging target for observers at northern latitudes.
Galaxy — Messier 83
The Southern Pinwheel Galaxy (M83, NGC 5236) is a beautiful barred spiral galaxy approximately 15 million light-years away.
With an apparent magnitude around 7.5, it is one of the brighter galaxies visible from Earth, although its southern position makes it difficult to observe from Britain.
M83 is especially notable for its well-defined spiral arms, active star-forming regions, and numerous recorded supernovae. Long-exposure photographs reveal a bright central bar surrounded by sweeping spiral arms containing young stars and glowing gas clouds.
The galaxy was discovered by Nicolas-Louis de Lacaille in 1752 and later included in Charles Messier’s catalog.
Ghost of Jupiter — NGC 3242
The Ghost of Jupiter (NGC 3242) is a planetary nebula approximately 1,400 light-years away, with an apparent magnitude around 8.6. Its name comes from its roughly circular appearance and apparent size, which can resemble Jupiter through a small telescope.
The nebula was formed when an aging star expelled its outer layers, leaving behind a hot stellar remnant that illuminates the surrounding gas.
Through larger telescopes, its bluish-green appearance and layered structure become more apparent.
Hydra Galaxy Cluster — Abell 1060
The Hydra Galaxy Cluster (Abell 1060) is a rich collection of galaxies approximately 190 million light-years away. Its prominent members include the giant elliptical galaxies NGC 3309 and NGC 3311, along with the spiral galaxy NGC 3312.
The cluster is part of the larger distribution of galaxies associated with the Hydra–Centaurus region and is an important target for studies of galaxy evolution and dark matter.
Tombaugh’s Globular Cluster — NGC 5694
NGC 5694 is a distant, compact globular cluster discovered by William Herschel in 1784. Clyde Tombaugh later helped establish its nature as a globular cluster, giving rise to its familiar nickname.
It is a faint target, best suited to observers with larger telescopes under dark skies.
Meteor Showers Associated With Hydra
Two minor meteor showers have been associated with Hydra: the Alpha Hydrids and Sigma Hydrids.
The Alpha Hydrids have been reported during January, while the Sigma Hydrids are active during December.
Neither is considered a major annual meteor shower, and both generally produce low meteor rates compared with more reliable displays such as the Geminids and Perseids.