The constellation of Hydra, the Sea Serpent // E. Slawik/NOIRLab/NSF/AURA/M. Zamani
Click below for an annotated image of the longest constellation in the sky, as well as some info about its history and named stars.
Hydra, which is Greek for "sea snake," is the longest and largest constellation in the night sky. For comparison, it would take about 500 full moons stretched end to end across the sky to cover the length of Hydra!
Although set down by the Greek astronomer Ptolemy in the 2nd century, the origins of this constellation can be traced back to the Babylonians. They saw this also as a hybrid of a serpent, lion, and bird. To the ancient Greeks, Hydra could be the snake that a crow served Apollo in a cup in lieu of water, or the dreaded monster Hydra that Hercules slayed as part of his twelve labors.
The named stars in Hydra are, in order of brightness:
Alphard (α Hydrae), an orange giant star about 177 light years away. Its name comes from the Arabic word al-fard meaning "the individual," since there are no other bright stars near it. Fun fact: Alphard appears on the flag of Brazil!
Naga (γ Hydrae) is a binary star system about 134 light years away. The primary star is a yellow giant. Its name comes from the Sanskrit word nāga meaning "serpent." Naga also appears on the Brazilian flag.
Ashlesha (ε Hydrae) is a quadruple star system about 129 light years away. The primary pair consists of a yellow giant and a yellow-white star. The name comes from the Sanskrit word Āśleṣā meaning "the embrace," referring to a constellation in Indian astronomy.
Ukdah (ι Hydrae) is an orange giant star about 263 light years away. Its name comes from the Arabic word uqdah meaning "knot."
Zhang (υ¹ Hydrae) is a solitary yellow giant star about 264 light years away. It has one confirmed brown dwarf orbiting it. Its name comes from Chinese astronomy, the constellation Zhāng Xiù (張宿) meaning "extended net."
Solitaire (E Hydrae) is a solitary orange giant star about 290 light years away. Its name is a reference to the obsolete constellation Turdus Solitarius, Latin for "solitary thrush." This in turn was named after the Rodrigues solitaire, an extinct flightless bird native to the island of Rodrigues, east of Madagascar. You can see this bird in the illustration above!
Minchir (σ Hydrae) is a solitary orange giant star about 370 light years away. Its name comes from the Arabic phrase minkhar ash-shujāʽ meaning "the nostril brave one."
Felis (HD 85951) is a solitary orange giant star about 570 light years away. Its name refers to the obsolete constellation Felis, Latin for cat. You can see the cat in the illustration above!
Lerna (HAT-P-42) is a solitary Sun-like star about 1,350 light years away. It has one confirmed exoplanet orbiting it, about the same mass as Jupiter, named Iolaus. Both names were given by the people of Greece: Lerna is the name of the lake where the Hydra lived, and Iolaus was the nephew of Hercules that helped him slay the beast.
Filetdor (WASP-166) is a solitary Sun-like star about 373 light years away. It has one confirmed exoplanet orbiting it, about 32 times more massive than Earth, named Catalineta. Both names were given by the people of Spain: both are characters in a Mallorcan folktale about a golden sea serpent.
