Epoch J2000 Equinox J2000
|Right ascension||19h 52m 28.36775s|
|Declination||+01° 00′ 20.3696″|
|Apparent magnitude (V)||3.87 (3.5 to 4.4)|
|Spectral type||F6 Ibv|
|U−B color index||+0.51|
|B−V color index||+0.89|
|R−I color index||+0.47|
|Variable type||Cepheid variable|
|Radial velocity (Rv)||–14.8 km/s|
|Proper motion (μ)||RA: +6.91 mas/yr
Dec.: –8.21 mas/yr
|Parallax (π)||2.36 ± 1.04 mas|
|Distance||approx. 1,400 ly
(approx. 400 pc)
|Mass||9.3 ± 0.4 M☉|
|Radius||66 ± 22 R☉|
|Surface gravity (log g)||1.5 cgs|
|Metallicity [Fe/H]||+0.10 dex|
|Age||26.4 ± 3.1 Myr|
Bright Star Catalogue (5th rev. ed.)
Eta Aquilae (η Aql, η Aquilae) is the Bayer designation for a star in the equatorial constellation of Aquila, the eagle. It was once part of the former constellation Antinous. On average, this star has an apparent visual magnitude of 3.87, making it one of the brighter members of Aquila. Based upon parallax measurements made during the Hipparcos mission, this star is located at a distance of roughly 1,382 light-years (424 parsecs), although the parallax estimate has a 44% margin of error.
This is a Cepheid variable star, with an apparent magnitude that ranges from 3.5 to 4.4 over a period of 7.176641 days. Along with Delta Cephei, Zeta Geminorum and Beta Doradus, it is one of the most prominent naked eye Cepheids; that is, both the star itself and the variation in its brightness can be distinguished with the naked eye. Some other Cepheids such as Polaris are bright but have only a very small variation in brightness.
At the relatively young age of 26 million years, this massive star has burned through the hydrogen fuel at its core and evolved into a supergiant, giving it a baseline stellar classification of F6 Ibv. The Ib luminosity class indicates this is a less luminous type of supergiant, while the 'v' suffix shows that the spectrum of the star varies. The periodic pulsations of this star actually cause the stellar class to vary between (F6.5–G2)Ib over the course of each cycle.
Compared to the Sun, Eta Aquilae has around 9 times the mass, roughly 66 times the radius, and is radiating 11,474 times as much luminosity. This energy is being emitted from the outer envelope at an effective temperature of 6,000 K, giving it the yellow-white hued glow of an F-type star. The radius of the star varies by 4.59 × 106 km (0.007 R☉) over the course of a pulsation cycle. Compared to its neighbors, this star has a high peculiar velocity of 16.7 ± 6.9 km s−1.
In Chinese, 天桴 (Tiān Fú), meaning Celestial Drumstick, refers to an asterism consisting of η Aquilae, θ Aquilae, 62 Aquilae and 58 Aquilae. Consequently, η Aquilae itself is known as 天桴四 (Tiān Fú sì, English: the Fourth Star of Celestial Drumstrick.)
This star, along with δ Aql (Denebokab) and θ Aql (Tseen Foo) were Al Mizān (ألميزان), the Scale-beam. According to the catalogue of stars in the Technical Memorandum 33-507 - A Reduced Star Catalog Containing 537 Named Stars, Al Mizān were the title for three stars :δ Aql as Al Mizān I,η Aql as Al Mizān II and θ Aql as Al Mizān III.
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- Eta Aquilae
- Image Eta Aquilae