Aquila Flies High in September

by Rod Kennedy

As August gives way to September, the fast paced heat of summer gives way to cooler, more relaxed evenings.  As the days and nights moderate and cool, the atmosphere steadies making for wonderful observing conditions.  The bright stars of summer slowly begin to work their way west and the bright stars of winter are just barely peeking above the horizon after midnight.  Yet one of the brightest constellations of the Summer Triangle is still easily visible almost at the zenith.

Aquila (ACK-will-uh) the Eagle is the last constellation that forms part of the Summer Triangle.  Its brightest star Altair (al – TARE) lies southwest of Deneb (DEN – ebb) within the cloud of the Milky Way.  Altair has a magnitude of 0.75 so it is very bright in the night sky.  Altair is very bright because it is fairly close to our solar system, only sixteen light years distant.  It is also a hotter, more luminous star than our sun.  Altair is a type A  star eleven times brighter than the sun.  The next two brightest stars in Aquila are Tarazed (TAR-a-zed) and Alshain (al-SHAIN). These two stars lie to the west and east of Altair respectively.  However, while Altair shines at a brilliant 0.75 magnitude, Tarazed and Alshain are only magnitude 2 and 3.  Under light polluted skies these two stars may be almost invisible, but under dark skies they will be fairly obvious so close to Altair.

Aquila was the focus of much attention on June 8, 1918.  A brilliant nova suddenly lit up the sky.  Over a period of several hours the nova had become brighter than the star Sirius in the winter sky.  This nova was the brightest “new star” since the great supernova of 1604.  The difference between a nova and a supernova has nothing to do with brightness but rather in process.  A supernova is the violent explosion of a massive star that has reached the end of its life.  A nova is a flaring of the outer layers of a star or the flashing of gases as one star spills material onto a companion.  A super nova is generally a one time event, while a nova can occur periodically.

For those looking for a less obvious constellation, one whose name may be obscure, scan the sky in the region between Cygnus (SIG-nus) the Swan and Aquila.  Here we find the small, faint constellations Delphinus (del-FIN-us) the Dolphin.  Delphinus is a neat little diamond shape that is easy to pick out under moderately dark skies.

September offers a wonderful target in Cygnus to deep sky observers looking for a challenge.  Just eight degrees south of Alberio (al-BEER-e-oh) is M27, the Dumbbell Nebula.  This is a classic example of a planetary nebula, the outer layers of a mid-sized star that have been gently puffed out into space.  M27 is a close planetary nebula (relatively speaking) at a distance of only 1000 light years.  Dark, steady skies and a good star chart or computer program will be necessary to spot the faint wisps of gas expelled from the dying star.  A small telescope should reveal the distinct structure of this deep sky gem.

The skies of fall are typically dark with very few bright stars.  Yet the bright stars of the Summer Triangle are still in prime positions near the zenith to offer good observing.  The moderating of temperatures should reduce the turbulence caused by convection.  This should make binocular and telescope observing easier.  And Aquila’s positioning in the Milky Way makes it a great place to look for deep sky objects.

September 2011 Chart

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