Constellation, Hya
Hydra: the Female Water Snake
Hydra covers 1,299 square degrees of sky, the 1st largest of the 88. Its brightest star is Alphard. It is best placed in the evening sky in April.
Hydra at a glance
| Fact | Value |
|---|---|
| IAU abbreviation | Hya |
| Meaning | the Female Water Snake |
| Pronounced | HIGH-druh |
| Genitive, used in star names | Hydrae (for example a Bayer name such as α Hydrae) |
| Area | 1,299 square degrees, number 1 of 88 by size |
| Stars to magnitude 6 in our catalogue | 121 |
| Brightest star | Alphard, magnitude 2.0 |
| Best seen | Evenings in April, when it is highest at 9 pm |
| Declination range | -36° to 7° |
| Borders | Centaurus, Antlia, Sextans, Crater, Pyxis, Virgo, Libra, Cancer, Corvus, Puppis, Monoceros, Canis Minor, Leo |
Where on Earth you can see Hydra
Hydra spans declinations -36° to 7°. Every part of it rises above the horizon at some moment for observers between latitudes 83°S and 54°N. Some of it can be seen from every latitude. This is geometry only: it ignores haze, hills and buildings near the horizon.
From six cities
| City | Latitude | Visibility | Middle at its highest |
|---|---|---|---|
| Pune | 18.5°N | All of it rises | 52° |
| New York | 40.7°N | All of it rises | 29° |
| London | 51.5°N | All of it rises | 19° |
| Tromsø | 69.6°N | Only part of it rises | 0° |
| Tokyo | 35.7°N | All of it rises | 34° |
| Sydney | 33.9°S | All of it rises | 76° |
Hydra's named stars
These stars in Hydra have names approved by the IAU Working Group on Star Names. Magnitude is brightness: a lower number is brighter, and the faintest stars seen with the naked eye on a dark night are about magnitude 6.
| Star | Designation | Magnitude | Distance (light-years) |
|---|---|---|---|
| Alphard | α Hydrae | 1.99 | 180 |
| Ashlesha | ε Hydrae | 3.38 | 130 |
| Ukdah | ι Hydrae | 3.90 | 260 |
| Zhang | υ1 Hydrae | 4.11 | 260 |
| Minchir | σ Hydrae | 4.45 | 370 |
| Felis | HR 3923 | 4.94 | 610 |
Distances are about, from the HYG database (Hipparcos parallax), and "not known" means the catalogue has no reliable parallax for that star.
How these facts were found
The name, meaning and boundaries are the IAU's. Area, borders and the latitude ranges are computed from those boundaries; the brightest star and the star count come from a magnitude-6 star catalogue; star names are matched to the catalogue by Hipparcos number and checked by position. The month is when Hydra's middle crosses the north-south line of the sky at 9 pm local solar time. See How we know.
Sources
- IAU: The Constellations. Names, meanings, pronunciations and boundaries
- IAU Working Group on Star Names. The official names of stars
- astronomy-engine. The MIT licensed library that does the calculations, run on the page's build machine and in the app
- HYG database v4.4 (astronexus). Distances, spectral types and luminosities, licence CC BY-SA 4.0