The Celestial Eagle Soars High in the Sky
Constellations, otherwise known as groups of stars that allegedly make pictures in the sky, have been dreamed up by humankind throughout the centuries, and depending on the culture, they can be all kinds of things.
Constellations can represent people, monsters, gods, instruments and much more. Almost a hundred years ago, the International Astronomical Union developed a standard list of 88 constellations, most from Greek and Roman mythology tales. Eight of these constellations are birds. Aquila the Eagle is one of the best bird constellations, and in late August and early September, it flies high in the southern early evening sky.
The best way to find Aquila in the Butler night sky is to use the handy tool known as the “Summer Triangle,” which is a prominent asterism formed by the three bright stars Vega, Deneb and Altair. Just look for the three brightest stars you can see high in the southeast sky in the early evening this time of year, and that’s it, the big triangle.
Each of these stars is the brightest in their own respective constellations. The highest and brightest star is Vega, the brightest star in the constellation Lyra the Harp. On the lower left is Deneb, the brightest star in the Cygnus the Swan. The star on the lower right of the Summer Triangle is Altair, the brightest shiner in Aquila the Eagle.
As you can see in the diagram, Altair is on the left-hand point of a large vertical diamond that, without too much imagination, outlines the wingspan of the heavenly eagle. Altair is at the heart of the eagle. To the right of the star on the right side of the diamond, you’ll see a faint line of stars that outline the tail of Aquila. The head of the eagle is on the left side of Altair, but you’ll have to rely totally on your imagination to see it. There are no real stars in that part of Aquila to help you.
Altair is the 12th brightest star in the sky, and it’s relatively close, only 16 light-years or about 97 trillion miles away. Believe it or not, that’s much closer than most stars in the night sky. Because it’s so close, astronomers know quite a bit about it. Altair is almost one and a half million miles in diameter, twice as large as our sun but cranking out a lot more light than our home star, more than 10 times as much.
The most fascinating discovery made about Altair is that it has a bulging waistline. The Palomar Observatory in California discovered that Altair’s diameter is more than 20% larger along its equator than from pole to pole. Further observations revealed that Altair is rapidly spinning on its axis at the rate of one full rotation in less than nine hours. By comparison, our sun takes more or less an entire month for one rotation. Like all other stars, Altair is a big ball of gas, so its rapid spinning and centrifugal force — the same force you feel on a fast merry-go-round — causes it to bulge out at its equator something fierce.
Scan your telescope all around Aquila, and you’ll find some lovely little star clusters of young stars, but the best eye candy through a small to moderately sized telescope is Messier object 11, otherwise known as M11, which is just off the tail of Aquila.
M11, as it’s referred to, is technically in a small adjacent constellation called Scutum the Shield. M11 is a beautiful open cluster of almost 3,000 stars, over 6,000 light years, or a little over 35,000 trillion miles away! They’re estimated to be very young stars, around 220 million years old, making them infants as far as star lifetimes go. M11 is called the “Wild Duck Cluster” because many people see it as a flock of flying ducks. Crank up your imagination to see that image!
One of the leading Greek mythology stories about Aquila has the eagle as Zeus’ faithful pet.
Zeus, of course, was the king of the gods of Mount Olympus. Aquila accomplished many missions for Zeus, including torturing enemies and delivering thunderbolts.
The eagle’s main claim to fame was his capture of the Trojan shepherd boy Ganymede, son of King Tros, to become the cupbearer of the gods on Olympus.
Zeus wanted the finest young man he could find to become the bartender of the gods. He sent Aquila on a reconnaissance mission where he discovered Ganymede, plucked him up by the shoulders, and delivered him to Zeus. Ganymede proved worthy of his forced labor, and happy hour was great on Mount Olympus ever after. Zeus rewarded his faithful eagle by placing him among the stars as the constellation we now see high in the southeast sky.
Incidentally, it’s no coincidence that one of Jupiter’s largest moons is named Ganymede since Jupiter is the Roman name for Zeus. The planet Jupiter is available in the sky right now, but it doesn’t get high enough to see in the eastern sky until after midnight, but it’s worth the wait!
Mike Lynch is an amateur astronomer and retired broadcast meteorologist for WCCO Radio in Minneapolis/St. Paul. He is the author of “Stars: a Month by Month Tour of the Constellations,” published by Adventure Publications and available at bookstores and adventurepublications.net. Contact him at mikewlynch@comcast.net.
