Aquila,
the Eaglesoars along the Milky Way, with its bright star Altair marking one vertex of the familiar Summer Triangle. Early evenings in September are good times to recognize and know this fine constellation.
Of the several birds represented by the mythology of the heavens, only Aquila flew there with his own powerful wings. Cygnus, the Swan, Corvus, the Raven, and Lyra (in the past known as a Vulture) were all placed in the sky by the gods of Mount Olympus. The early seventeenth century German astronomer Johann Bayer, the first to publish an organized chart of the constellations—the Uranometria—added the southern constellations Grus, the Crane, Tucana, the Toucan, Avis Indicia (now Apus, the Bird of Paradise), Pavo, the Peacock, and the miraculous Phoenix. Columba, the Dove, was known to Bayer and others, but was not established until 1679 by Augustin Royer.
Altair is the brightest star in the constellation; and, flanked by Alshain (Beta-Aquilae) and Tarazed (Gamma-Aquilae), the trio are known as the Family of Aquila and form a pretty, recognizable straight-line group of stars. Altair is a remarkable star. It is one of the closest bright stars and has a large proper motion. It is also known as having an exceptional rotational rate, measured by the broadening of its spectral lines. This effect comes about by the Doppler shifting of the approaching and receding limbs of the star. It turns about three times in one of our days, compared to one turn in 25 days for our Sun.
Aquila is a worthy site for binocular viewing. In addition to a number of double stars to be found, there is an open cluster of stars, NGC 6709, that can be seen against a rich background of other, Milky Way stars. The star Eta Aquilae is a supergiant Cepheid variable which brightens from magnitude 4.4 to 3.5 and dims again with a period of just over a week’s time.
The interstellar dust clouds Barnard 142 and 143 are about 1½ degrees west of the star Gamma-Aquilae (the bright star in the photo), which is about 2" northwest of Altair (lower corner). B143 is about a half-degree in size and has the shape of a broad, short-handled, tuning fork with the “prongs” pointed westward. To the south is B142, a linear-shaped dark nebula underlining B143. Together, these two resemble a sort of celestial letter E, and so is sometimes called Barnard's E nebula. These dark nebulae, which are from 1000 to 3000 light years distant, can be seen with a pair of binoculars under clear, dark, non-polluted skies. The photo is by Conrad Jung. [The photo will be supplied when available.]
In Greek legend, there was a terrible struggle between the giant Titans and the Olympian gods, who were led by Zeus. (Zeus was later known in Roman culture as Jupiter.) In this war it was the eagle who carried the thunderbolts which were instrumental along with the blinding lightning of the Cyclops in defeating the Titans. At war’s end Zeus was declared Sovereign of the World, and he kept the eagle with him always.
Across the Milky Way from the bright star Altair one finds the even brighter star Vega in the constellation Lyra. There is a charming story from the Orient that explains why these two are on opposite sides of the Milky Way. Chih Nu was the Chinese goddess of weaving, who worked sunlight and shadow into the wondrous tapestries of the constellations. One day as she looked from her castle window over the river of heaven she saw a handsome youth who was tending the royal oxen. Their eyes met and the two fell deeply in love. Her father, the sun-king, welcomed the match, for Ch’ien Niu, the young herdsman, was a fine worker and kind to the animals. Chih Nu made her wedding dress from cloth woven of starlight and dewdrops, and the two were very happy in their marriage. But the lovers began to neglect their work and lazed on the banks of the starry river in devotion only to each other. The sun-king could not control their actions and finally banished Ch’ien Niu to the far side of the wide river, and sent Chih Nu back to her weaving at the castle. They begged for forgiveness, but the king would only allow them to see each other once every year, on the seventh day of the seventh month, but they must find their own way across the river.
And so Chih Nu asked the birds of heaven, the magpies, to help her. Ever since, on this one day, magpies all gather together and form a bridge with their wings for the lovers to use in crossing the Milky Way. In China and Japan on July 7th there is not a magpie to be found—they are all away building the bridge. If one should be seen, the children may chase it away, since the bird is surely neglecting its duty.