Definition
Epsilon Aquarii (ε Aquarii) is a star designated by the Bayer system within the constellation Aquarius. It is also recognized by the proper name Albali.
Overview
Epsilon Aquarii is a blue‑white star visible to the naked eye with an apparent visual magnitude of approximately 4.0. It lies near the celestial equator, making it observable from both northern and southern latitudes. The star is cataloged in multiple astronomical references, including the Henry Draper Catalogue (HD 203280) and the Hipparcos catalogue (HIP 105560). The International Astronomical Union’s Working Group on Star Names (WGSN) officially approved the name Albali for ε Aquarii in 2017.
Etymology / Origin
The name Albali is derived from Arabic. Its precise linguistic root is not definitively established, but it is commonly interpreted as stemming from the Arabic word “al‑bali” (الـبالي), which may refer to a “swallow” or “bird” in traditional celestial nomenclature. The Bayer designation “ε” originates from the 1603 star atlas of Johann Bayer, who assigned Greek letters to stars within each constellation roughly in order of brightness.
Characteristics
- Spectral Type: B9 IV (subgiant) or B8 V (main‑sequence), depending on the source; the star exhibits the blue‑white hue typical of late B‑type stars.
- Apparent Magnitude (V): ~4.0, making it faintly visible without optical aid.
- Absolute Magnitude (V): Approximately –0.6, indicating a luminosity several hundred times greater than that of the Sun.
- Distance: Parallax measurements from the Hipparcos and Gaia missions place ε Aquarii at roughly 210 light‑years (≈ 65 parsecs) from the Solar System.
- Mass and Radius: Estimates suggest a mass of about 3 M☉ (three times solar) and a radius of roughly 2.5 R☉.
- Luminosity: The star radiates on the order of 150 L☉ (solar luminosities).
- Effective Temperature: Approximately 11,500 K, consistent with its B‑type classification.
- Rotation: The projected rotational velocity (v sin i) is measured at around 120 km s⁻¹, indicating relatively rapid rotation for a star of its type.
- Variability: ε Aquarii is not known to be a variable star; photometric observations report stable brightness within measurement uncertainties.
- Companionship: No confirmed stellar companions have been detected; however, some surveys have listed it as a possible single star, while others note a distant visual companion of much lower brightness, though physical association remains unverified.
Related Topics
- Bayer Designation – The system of assigning Greek letters to stars within a constellation based on relative brightness.
- Constellation Aquarius – A zodiacal constellation representing the water‑bearer; ε Aquarii is one of its notable stars.
- Star Naming Conventions – The International Astronomical Union’s processes for standardizing proper names for stars, such as the approval of Albali.
- B‑type Stars – A class of hot, massive stars with spectral types ranging from B0 to B9, characterized by strong hydrogen absorption lines and blue‑white coloration.
- Hipparcos and Gaia Missions – Space‑based astrometric projects that have provided precise measurements of stellar positions, parallaxes, and proper motions, including data for ε Aquarii.
Note: All presented data are derived from peer‑reviewed astronomical catalogs and the International Astronomical Union’s star‑naming records. Where multiple classifications exist, the most widely cited values are indicated.