The birds flying among the stars of the night sky

Saturday, Oct 9, 2021 4:00 AM

Greetings, stargazers.

Aquila, the Eagle, may not be the most well-known, or most recognizable constellation, but it is straightforward to find, and is worth adding to your repertoire.

It is one of the 48 constellations listed by Ptolemy, and because it is found along the Milky Way, it has numerous dim background stars and some prominent open star clusters within its borders.

In ancient mythology, Aquila was the eagle that carried Zeus’ thunderbolts. In other cultures, it was seen as either an eagle, a vulture or a falcon, and the name of the brightest star, Altair, is from the Arabic phrase for the flying eagle. With a bit of connect-the-dots imagination, it isn’t hard to see a bird of prey flying north along the Milky Way.

The next big constellation in the direction of Aquila’s flight is Cygnus, the swan, which is flying south with its long, outstretched neck heading toward the eagle. I haven’t found references to any predatory avian conflicts in mythology, but I did see one suggesting that Aphrodite was disguising herself as an eagle to amorously pursue Zeus, who was at the time in the form of a swan. Feel free to make up your own story.

The brightest star, Altair, at magnitude 0.76 is the 12th brightest star in the night sky. It is the southernmost of the three stars of the summer triangle, which might be the easiest way to identify Altair.

Another way to find it is to know it is a few degrees north of the celestial equator, and at 8 p.m. it will be transiting the meridian 60 degrees above the southern horizon. This places Altair about twice as high as the slightly brighter Saturn. Jupiter, a bit to the east in the southern sky, is significantly brighter than either Saturn or Altair.

Because Aquila is along the Milky Way, a scan of the constellation with binoculars will show a rich collection of background stars. There are numerous open clusters, but most of them are too diffuse to stand out among the rich background.

The Wild Duck cluster, or M11, is just outside the boundary of Aquila, but I usually associate that cluster with this constellation because I use the stars in the tail of the eagle as pointers to it. M11 is one of my favorite open clusters because it is bright enough to be barely visible to the naked eye, and it nicely fits in a medium-power eyepiece. It is one of the most massive open clusters and is dense enough to stand out even among the numerous background stars in the field of view.

This month

Venus, the evening star, will reach its easternmost elongation, when it will be the highest in the evening sky, on Oct. 29. With a low-power telescope it should easily show as a half-disk.

Mercury reaches its westernmost elongation, when it will be the highest in the eastern sky before sunrise, on Oct. 25.

Jupiter and Saturn continue to dominate the southern sky, and both will make excellent binocular or telescope targets all month.

The Orionid meteor shower peaks Oct. 21, but the full moon this month on Oct. 20 will probably wash out the view of most shooting stars.

Charles Hakes teaches in the physics and engineering department at Fort Lewis College and is the director of the Fort Lewis Observatory. Reach him at hakes_c@fortlewis.edu.