The Constellations of the Summer Triangle

Stars from three constellations in the northern hemisphere form an imaginary triangle – the Summer Triangle, which is an asterism. The constellations Aquila, Cygnus, and Lyra contain the stars Altair, Deneb, and Vega. Together these stars create a nightly picture of a triangle in space.

The Summer Triangle

As you would expect, given its name, the Summer Triangle predominates the sky during the summer season. However, the constellations of the summer triangle can be seen for at least a portion of the night at any time during the year (in mid-northern latitudes). This asterism is a large triangle formed by the three first-magnitude stars Altair, Deneb, and Vega. It is best seen during northern summer and autumn evenings.

In the constellation Aquila

Altair is the brightest star located in the constellation Aquila and it forms one vertex of the Summer Triangle. It has a magnitude 0.76 making it the the twelfth-brightest star in the sky. It is a spectral class A7 dwarf star and it is 16.8 light years away. (The spectral classification in astronomy, is a classification of the stars by their temperature and spectrum.)

Other facts about Altair:

Astronomical Name: Alpha Aquilae.

Meaning: From Arabic: “The Eagle”.

Apparent Magnitude: 0.76.

Absolute Magnitude: 2.20.

Distance (light-years): 16.8.

Altair is easily recognized, because it is situated on either side along a straight line by two stars, Alshain and Tarazed (Beta and Gamma Aquilae). It is also one of the nearest bright stars and it has an exceptional rotation rate. Using Doppler shift measurements, it rotates more than three times on its axis in one of our days, as compared to one rotation in 25 days for our Sun.

Other points of interest. There are nine main objects in the constellation:

Altair, the Flying One (one of the stars in the Summer Triangle)

Alshain, the Falcon

Tarazed, the Plundering Falcon

Deneb El Okab “Tail of the Falcon”

Deneb Zeta

Bezek “lightning”

Tseen Foo “The heavenly raft”

Al Thalmain The two ostriches
Eta
Iota
Source: http://www.brighthub.com/science/space/articles/95010.aspx