Aquila - The Eagle

Aquila is a prominent constellation in the northern-hemisphere summer sky, best seen from July through October. Aquila forms a triangle in the heavens which rises to the zenith in late summer. It lies along the summer Milky Way, south of Cygnus the Swan. Aquila is flanked by Aquarius, Hercules, and Ophiuchus.

History and Mythology

Aquila is believed to be the eagle that held the thunderbolts for Zeus, king of the gods. Aquila was sent to kidnap Ganymede, a shepherd boy, who was taken to Mount Olympus to become a cup-bearer for the gods. Aquila has been associated with birds since the triangular outline seems to describe a bird with outstretched wings.

Asian mythologies identify the bright star Altair in Aquila as Ch'ien Niu, the herdsman who watched over the royal herds. He fell in love and married Chih Nu. They soon neglected their duties, and her father the sun king, Vega, was so angry with them that he made them spend their lives on opposite sides of the Milky Way. It is said that once a year on the seventh day of the seventh month, if the weather is clear, Magpies will spread their wings across the river for the two to meet. If it rains, they cannot meet. The Japanese celebrate this as a festival called Tanabata.

Notable Objects

The most prominent star in Aquila is Altair. It is called the Eagle Star, and it is the 12th brightest star in the sky. Yellow-white Altair is ten times more luminous than our sun, and is at a distance of about 16 light-years. It forms a corner of the Summer Triangle along with the stars Vega and Deneb in the constellations Lyra and Cygnus. Altair is also known to be one of the fastest-rotating stars, with a rotation period under 10 hours.

The prominent trio of Alpha, Beta, and Gamma Aquliae reminded the Arabs of a beam scale, or balance. Alshain, or Beta Aquilae, has a Persian name which means "balance", and is about 45 light years away. Gamma Aquilae, Tarazed, also has a Persian name meaning "the beam of the scale". It is an orange giant star 460 light years away.

Eta Aquilae is one of the sky's most prominent Cepheid variables, discovered in 1784. The variations of this star are obvious, changing from magnitude 3.5 to 4.3 and back again over a period of 7.2 days.

NGC 6709 is a large open cluster with little central condensation. It can be seen with an 8-inch or larger telescope. Another cluster visible in moderate telescope is the 8th-magnitude NGC 6755. There are a few planetary nebulae in Aquila, but they are 11th magnitude and fainter, making them difficult to find without at least a 10-inch telescope. The brightest of these is NGC 6781, with a bright, circular disk 1.8 arcminutes in diameter.