✦ Hydra (Hya)
✦ Hydra (Hya)
Subfolder of: Fixed Stars · Constellations
| Field | Value |
|---|---|
| IAU name | Hydra |
| IAU abbreviation | Hya |
| Latin genitive (used in Bayer names) | Hydrae |
| Zodiacal constellation | No |
| Ptolemaic constellation | Yes — one of Ptolemy’s 48 (Almagest VII–VIII) |
Constellations are not the same as the tropical signs: the signs are 30° divisions measured from the March equinox, while constellations are IAU sky regions of unequal size. Precession has moved the constellations roughly one sign-width against the tropical zodiac since antiquity.
Vault stars in Hydra
| Star | Designation | λ J2000.0 | λ 2026.0 | V mag |
|---|---|---|---|---|
| Alphard | α Hydrae | 27°17′ Leo | 27°38′ Leo | 1.97 |
Sources
- IAU, The Constellations (88 official constellations, abbreviations): https://www.iau.org/public/themes/constellations/
- Swiss Ephemeris fixed-star catalogue
sefstars.txt(ICRS/Hipparcos-based positions, proper motions, magnitudes): https://github.com/aloistr/swisseph/blob/master/ephe/sefstars.txt — ecliptic longitudes computed for this vault with Astropy 8.0 (GeocentricMeanEcliptic, mean equinox of J2000.0 and of 2026-01-01) - Ptolemy, Almagest VII–VIII (star catalogue of 48 constellations), trans. G. J. Toomer (1984)