Hyades (star cluster)
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| Observation data (J2000.0 epoch) | |
| Constellation | Taurus |
| Right ascension | 4h 27m |
| Declination | +15° 52′ |
| Distance | 153 ly (47 pc) |
| Apparent magnitude (V) | 0.5 |
| Apparent dimensions (V) | 330′ |
| Physical characteristics | |
| Mass | 400 M☉ |
| Radius | 10 light years (core radius) |
| Estimated age | 625 million years |
| Other designations | Melotte 25, Collinder 50, Caldwell 41 |
The Hyades (/ˈhaɪ.ədiːz/; Greek Ὑάδες, also known as Melotte 25 or Collinder 50) is the nearest open cluster to the Solar System and one of the best-studied star clusters. The Hipparcos satellite, the Hubble Space Telescope, and infrared color–magnitude diagram fitting have been used to establish a distance of ~153 ly (47 pc) to the cluster center. The distances established by these three independent methods agree, thereby making the Hyades an important rung on the cosmic distance ladder. The cluster consists of a roughly spherical group of hundreds of stars sharing the same age, place of origin, chemical content, and motion through space. From the perspective of observers on Earth, the Hyades Cluster appears in the constellation Taurus, where its brightest stars form a "V" shape along with the still brighter red giant Aldebaran. However, Aldebaran is unrelated to the Hyades, as it is located much closer to Earth (hence its apparent brightness) and merely happens to lie along the same line of sight.
The five brightest member stars of the Hyades have all evolved away from the Main Sequence and now lie at the bottom of the giant branch. Four of these stars, with Bayer designations Gamma, Delta 1, Epsilon, and Theta Tauri, form an asterism that is traditionally identified as the head of Taurus the Bull. The fifth of these stars is Theta-1 Tauri, a tight naked-eye companion to the brighter Theta-2 Tauri. Epsilon Tauri, known as Ain (the "Bull's Eye"), has a gas giant exoplanet candidate, the first planet to be found in any open cluster.
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