It will be fairly dark at 9 tonight and a good time to look for the summer triangle of Altair, Deneb and Vega.
Let’s start first with Altair in Aquila the Eagle. Look directly east a little after 9 p.m. and Altair will be 35 degrees above the horizon. Next, look toward the north (left) to find Deneb in Cygnus the Swan almost 40 degrees above the northeastern horizon. Completing the triangle is Vega in Lyra the Lyre, above Altair and Deneb about 61 degrees above the northeastern horizon.
Don’t be confused when I mention degrees above the horizon. Ninety degrees above the horizon is overhead. Thirty degrees is one-third of the way from the horizon to overhead; 45 degrees is halfway; and 60 degrees is two-thirds of the way from the horizon to overhead.
Altair, Deneb and Vega are bright stars and should be easily visible if you look in the right direction.
The stars of the Summer Triangle are blue or blue-white in color. They are not related to each other; they just happen to look close together. Vega, the fifth brightest star in the sky, is 25 light-years away with a large disk of gas and dust possibly containing planets. Altair, 17 light-years away, rotates so fast it is shaped like an egg. My favorite is Deneb, which is estimated to be roughly 1,425 light- years from Earth. Even so, Deneb is the 19th brightest star in the sky. Deneb is one of the most luminous stars in the entire Milky Way.