Altair, also known as Alpha Aquilae, is the brightest star in the constellation Aquila, the Eagle. It also ranks among the brighter stars in the northern sky. Altair spins on its axis rapidly, giving the star a flattened shape.
Altair is a main-sequence star. Such stars produce most of their energy by fusing (combining) hydrogen nuclei into helium nuclei in their cores (see Main-sequence star ). Altair has just begun the main-sequence phase of its existence.
Altair’s mass (amount of matter) is about 1.8 times that of the sun. Altair produces about 11 times as much power as the sun. Altair is 16.8 light-years distant from the Earth. A light-year is the distance that light travels in a vacuum in a year—about 5.88 trillion miles (9.46 trillion kilometers).
Altair appears white and is in the spectral class A (see Star (Spectral classes) ). It and two other spectral class A stars, Vega and Deneb, make up a well know grouping of stars called the Summer Triangle.
Astronomers learned that Altair is rotating fairly rapidly by analyzing the light coming from the star. In 2001, they detected that the star was significantly flattened. The flattening results from rapid rotation, the first time such an effect has been directly observed. In 2006, they determined that Altair, as well as Vega, was rotating only slightly slower than a rate that would cause it to break up.
