2013 09 Constellation of the Month – Aquila

Aquila, the Eagle is a fairly easy constellation to identify.  Along with last month's constellation of the month, Lyra, and the October 2012 constellation of the month, Cygnus, Aquila's brightest star, Altair makes up the large and prominent Summer Triangle of stars.  Aquila is the southernmost of these three constellations.

Altair is the 12^th brightest star in the night sky, at magnitude 0.77.  It is very close to use – only 16.3 light years away, or 4 times as far away as the closest star, Alpha Centauri.   Altair rotates very rapidly, at almost 300 kilometers per second – about 150 times faster than our Sun.  As a result of this rotation, Altair is not spherical, but is flattened at the poles.  

Aquila's immediate neighbors are small and rather faint constellations, such as Delphinus, Scutum, Vulpecula, Sagitta, Capricornus, and Equuleus.  The tail of Serpens points to Aquila from the East.  

The band of the Milky Way passes through Aquila on the way from Cygnus to the North and Sagittarius to the South.  When we look at the band of the Milky Way, we are looking along the plane of our disc-shaped galaxy.  As a result, we see many more starts than if we look above or below the plane.  We would also expect there to be many more nebulae and star clusters, but those in the line of sight of Aquila are relatively faint.  

Coincidentally, there are very few galaxies to be found looking in the direction of Aquila.  So, there are no Messier objects in Aquila.  The French astronomer Charles Messier cataloged a list of 110 hazy objects in the sky.  He was trying to identify these objects -- which appeared to stay in the same place -- in order to distinguish them from moving comets, for which he was searching.  The objects he cataloged turned out to be nebulae (clouds of gases) in our galaxy and distant galaxies themselves. But nothing in Aquila makes this Top 110.