アルタイル

Only 16.7 light-years from Earth, Altair ranks among the nearer bright stars, and that proximity carries it to apparent magnitude 0.76. It is Alpha Aquilae, the leading light of the constellation Aquila, and a white A-type star with a B–V colour index of 0.221. The star's absolute magnitude of 2.21 marks a fairly modest intrinsic brightness, so its conspicuousness rests largely on closeness. Set near the celestial equator at declination +8°, Altair is visible from almost every latitude and forms the southern vertex of the Summer Triangle alongside Vega and Deneb, a signpost of the northern summer sky.