AQUILA (ak´-wi-lä)—THE EAGLE, AND ANTINOÜS. (Face Southeast.)
Location.—Half-way up the sky in the Milky Way, you will see three stars in a line, the middle one much brighter than the other two. This bright star is Altair, in Aquila. It forms with Vega and Deneb an isosceles triangle. Altair is at the apex, about 35° from the other two. A triangle is formed by Vega, Altair, and Ras Alhague, in the Serpent Bearer, which is about 30° west of Altair.
This is a double constellation composed of Aquila and Antinoüs. Altair is in the neck of the Eagle, Alschain in the head of Antinoüs.
When the moon is absent, a rude arrowhead can be traced out, embracing almost all the stars in Aquila.
η is an interesting variable star, changing from magnitude 3.5 to 4.7 and back again within a period of 7 days 4 hours 12 minutes.
Altair rises about 8° north of the exact eastern point on the horizon.
In a.d. 389 a wonderful temporary star flashed out near Altair that equalled Venus in brightness and vanished within three weeks’ time.