Alcyone (star)
Brightest star in the Pleiades, a blue-white giant with a gaseous disk.
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Alcyone, also designated Eta Tauri, is a blue-white giant star and the brightest member of the Pleiades open cluster. At apparent magnitude 2.87, it is the third-brightest star in the constellation Taurus, located about 440 light-years from Earth. Its name comes from Greek mythology, where Alcyone is one of the seven daughters of Atlas and Pleione known as the Pleiades.
Quick Facts
- Bayer designation
- Eta Tauri
- Apparent magnitude
- +2.87
- Absolute magnitude
- −2.39
- Spectral type
- B7IIIe
- Distance
- ~440 light-years
- Effective temperature
- 12,258 K
- Bolometric luminosity
- 1,750 times solar
Facts from the source article.
Lore & Background
Alcyone is a B-type giant star, similar to other bright B-type stars in the Pleiades cluster. Its spectral type B7IIIe indicates the presence of emission lines, and like many Be stars, it has created a gaseous disk flung into orbit from its equator. The star rotates rapidly, causing an ellipsoidal shape; its effective radius is nearly ten times that of the Sun, with the equatorial radius larger than the polar radius. Its effective temperature is 12,258 K, though the actual temperature is greater at the poles and lesser at the equator.
The age of the Pleiades is typically calculated at around 130 million years, but Alcyone itself appears younger, less than 100 million years. It may be a blue straggler, or models may not derive an accurate age for stars of this type. In Chinese astronomy, Alcyone is part of an asterism called Hairy Head, which includes several other Pleiades stars, and its Chinese name means 'the Sixth Star of Hairy Head'.
Reader's Guide
Alcyone's significance lies in its role as the brightest and most luminous star in the Pleiades, one of the most recognizable open clusters in the night sky. Its variability has long been suspected, and a 2017 study using Kepler Space Telescope data found periodic brightness variations up to 0.001 magnitudes, with a 2.3-day period thought to be the rotation period. It has been classified as both a rotational variable and a slowly pulsating B-type star, though as of 2025 it has not been formally listed in the General Catalogue of Variable Stars.
The star has several cataloged companions: component B is 24 Tauri, a magnitude 6.28 A0 main-sequence star; component C is V647 Tauri, a δ Scuti variable star; and component D is a magnitude 9.15 F3 main-sequence star. The Washington Double Star Catalog lists four additional faint companions and describes component D as itself double. Some lunar occultation studies found evidence of sub-arcsecond companions, but a 2021 interferometric study concluded that Alcyone is a single star system.
More in Open Clusters
Sources
Compiled from Wikipedia and the sources listed below. Text from Wikipedia is available under CC BY-SA 4.0; this entry is adapted from it.
- Wikipedia: Alcyone (star) (CC BY-SA 4.0).
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