Aquila

Transit Date of principal star:
20 July

Aquila, The Eagle, is another ancient constellation whose history is linked to the Greek gods. The most often-told story is that of Hebe, daughter of Zeus and Hera, who married Heracles. Before her marriage Hebe was the goddess of youth and she appeared in ceremonies as the official cup bearer. (That's to say, in all religious functions, she was responsible for pouring the wine.) She gave up the post after her marriage (although some accounts say that in one ceremony she indelicately exposed herself and was promptly sacked). In any case, the position was open and Zeus sought a suitable replacement. Ganymede, a splendid Trojan prince, was Zeus's eventual choice. Zeus either disguised himself as an eagle or sent his Royal Eagle. Ganymede was plucked from his native land and taken to Mount Olympus where he became the wine-pourer for all the gods. This explains why Ganymede is Jupiter's brightest and largest companion: Jupiter of course being the Roman name for Zeus. The constellation Aquila is supposed to represent the eagle carrying away the youth. There are four or five fairly bright stars just below the asterism which are meant to represent the boy (this asterism is called "Antinous" but is not recognised any longer). Eventually Zeus put Ganymede's own image in the skies, as the god's water bearer, Aquarius. Aquila's Bayer stars are generally third and fourth magnitude, except Altair (alpha Aql), the twelfth brightest star. Altair spins very rapidly, completing one revolution every 6.5 hours, which deforms the star. It is thought Altair's equatorial diameter is twice its polar diameter. Double stars: Beta Aquilae is relatively fixed, with a faint red dwarf companion: 3.7, 11.6; PA 5º, separation 13". Zeta Aquilae also has a very faint dwarf companion, of uncertain period: 3.0, 12; PA 53º, separation 6.5". Pi Aquilae: 6, 7; PA 111º, separation 1.4". Chi Aquilae is a close binary with the separation slowly decreasing: 5.6, 6.8; PA 77º, separation 0.5". Variable stars: Eta Aquilae is a cepheid variable: 3.48-4.39 with a period of 7.18 days (more precisely 7 days, 4 hours, 14 minutes and 21.8 seconds). The magnitude changes very gradually throughout this time period, and is easily noticed with binoculars (using beta Aquilae, 3.7, as a reference). Sigma Aquilae is an eclipsing binary (EB type), fluctuating between 5.14 and 5.34 every 1.95 days. The combined mass is equal to twelve suns although their densities are each only about one tenth of the sun's. R Aquilae is a long period variable: 5.5 to 12 every 284.2 days. The 2000 maximum should occur on 4 June. Deep Sky Objects: NGC 6709 is a loose cluster comprised of about forty stars. It's approximately 2500 light years away and is located five degrees SW of zeta Aquilae. For a closer appreciation of Aquila, visit the Binocular Section.

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