Eta Aquarii, also named Fenmu, is a star in the equatorial constellation of Aquarius. The star is visible to the naked eye with an apparent visual magnitude of 4.04. The distance to this star, as determined by parallax measurements, is about . It is drifting closer to the Sun with a radial velocity of –8 km/s. Eta Aquarii is near the radiant of a meteor shower named the Eta Aquariids after it.
Naming Eta Aquarii is a Bayer designation that is Latinized from η Aquarii, and abbreviated Eta Aqr or η Aqr, respectively. This star, along with γ Aqr (Sadachbia), π Aqr and ζ Aqr, were al Aḣbiyah (الأخبية), the Tent.
In Chinese astronomy, (), meaning Tomb, refers to an asterism consisting of η Aquarii, γ Aquarii, ζ Aquarii, π Aquarii. 中國星座神話, written by 陳久金. Published by 台灣書房出版有限公司, 2005, . Consequently, the Chinese name for η Aquarii itself is (, .) AEEA (Activities of Exhibition and Education in Astronomy) 天文教育資訊網 2006 年 5 月 16 日 The IAU Working Group on Star Names approved the name Fenmu for Eta Aquarii on 17 September 2026.
Properties The stellar classification of Eta Aquarii is B9IV-Vn, which may indicate that it is beginning to evolve away from the main sequence into a subgiant as the supply of hydrogen at its core becomes exhausted. It is 65 million years old and is spinning rapidly with a high projected rotational velocity of 271 km/s. This rotation is causing an equatorial bulge, giving the star an oblate figure with a 24% larger radius at the equator than at the poles. The Doppler effect from the rapid rotation is causing the absorption lines in the star's spectrum to blur, as indicated by the 'n' suffix in the star's classification. Eta Aquarii has an estimated 2.96 times the mass of the Sun and 2.8 times the Sun's radius. The star is radiating 103 times the luminosity of the Sun from its photosphere at an effective temperature of 11,042 K.
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External links Image Eta Aquarii