Altair

Altair is Alpha Aquilae, apparent magnitude 0.77, and at 16.7 light years it is one of the nearest stars visible to the naked eye. It is a white main-sequence star, type A7, and it rotates so fast, a full turn in roughly nine hours, against the Sun's twenty-six days, that it is visibly flattened into an oblate spheroid, its equatorial diameter about a fifth greater than its polar. Interferometry has actually imaged this distortion and the resulting gravity darkening, making Altair one of the first stars other than the Sun to have its surface shape mapped. It is the southern vertex of the Summer Triangle, with Vega and Deneb. The name, al-nasr al-ta'ir, means the flying eagle.

Altair's oblateness was directly measured only in 2007, using long-baseline optical interferometry that combined light from several separated telescopes to synthesise the resolving power of a much larger instrument, a technique that has since been applied to several other fast rotators; before that the flattening was inferred from the rotation period and mass rather than seen directly. Altair's fast rotation also broadens its spectral lines considerably, a real observational consequence that made its true rotation rate difficult to pin down accurately before interferometric imaging settled the question directly.

Sources AstronomyAndrew Fraknoi, David Morrison, and Sidney C. Wolff (OpenStax) with Almagest (Mathematike Syntaxis)Claudius Ptolemy

Ptolemy in the Tetrabiblos gives the bright star of Aquila the nature of Mars with Jupiter, and the tradition that follows reads Altair for boldness, command and confidence, with a recurring caution about sudden or self-inflicted mischief, the martial half supplying the daring, the Jovian half the position it wins. The eagle is a fitting figure for it. In East Asian tradition Altair carries a quite separate story: it is the Cowherd of the Qixi legend, separated from the Weaver star Vega by the river of the Milky Way and permitted to cross to her once a year, a festival still kept in China and Japan.

The Qixi festival tied to Altair and Vega is kept on the seventh day of the seventh lunar month across China, Japan, Korea and Vietnam under various local names, Tanabata in Japan among them, and it is one of the clearer cases in this whole set of tables of a genuinely independent, non-Hellenistic interpretive tradition attached to a star that also carries a full Ptolemaic delineation, the two traditions running side by side without either having influenced the other. The Qixi and Tanabata festivals attached to Altair are unrelated to anything in the Ptolemaic or later Western fixed-star tradition, a genuinely separate interpretive layer resting on the identical star.