Alpha Gruis is the brightest star in the southern constellation of Grus. It is officially named Alnair; Alpha Gruis is the star's Bayer designation, which is Latinized from α Gruis and abbreviated α Gru. With an magnitude of 1.7, it is one of the brightest stars in the sky and one of the fifty-eight stars selected for celestial navigation. Alpha Gruis is a single, B-type main-sequence star located at a distance of . Nomenclature α Gruis (Latinised to Alpha Gruis) is the star's Bayer designation. (Its first depiction in a celestial atlas was in Johann Bayer's Uranometria of 1603.) It bore the traditional name Alnair or Al Nair (sometimes Al Na'ir in lists of stars used by navigators), from the Arabic al-nayyir "the bright one", itself derived from its Arabic name, al-nayyir min dhanab al-ḥūt (al-janūbiyy), "the bright one from the (southern) fish's tail" (see Aldhanab). Confusingly, Alnair was also given as the proper name for Zeta Centauri in an astronomical ephemerides in the middle of the 20th century. In 2016, the International Astronomical Union organized a Working Group on Star Names (WGSN) to catalog and standardize proper names for stars. The WGSN approved the name Alnair for this star on 21 August 2016 and it is now so entered in the IAU Catalog of Star Names. Along with Beta Gruis, Delta Gruis, Theta Gruis, Iota Gruis, and Lambda Gruis, Alpha Gruis belonged to Piscis Austrinus in traditional Arabic astronomy. In Chinese, (), meaning Crane, refers to an asterism consisting of Alpha Gruis, Beta Gruis, Delta2 Gruis, Epsilon Gruis, Zeta Gruis, Eta Gruis, Iota Gruis, Theta Gruis, Mu1 Gruis and Delta Tucanae. Consequently, Alpha Gruis itself is known as (, ). The Chinese name gave rise to another English name, Ke. Properties Alpha Gruis has a stellar classification of B6 V, although some sources give it a classification of B7 IV. The first classification indicates that this is a B-type star on the main sequence of stars that are generating energy through the thermonuclear fusion of hydrogen at the core. However, a luminosity class of 'IV' would suggest that this is a subgiant star; meaning the supply of hydrogen at its core is becoming exhausted and the star has started the process of evolving away from the main sequence. It has no known companions. The measured angular diameter of this star, after correcting for limb darkening, is . At a