Aquila, the Eagle, is a constellation of the celestial equator, one of Ptolemy's forty-eight, representing the eagle of Zeus, the bird that carried the god's thunderbolts and bore the youth Ganymede up to Olympus. Its brightest star, Altair, one of the nearest bright stars to the sun, forms with Vega and Deneb the Summer Triangle, and Altair itself means the flying eagle in Arabic. The constellation lies within the rich star fields of the Milky Way. In astronomical tradition it is a pattern of stars rather than a zodiac sign, set near the neighbouring bird constellations Cygnus the swan and the little Sagitta the arrow. These are the features of Aquila as the classical and modern traditions describe it, distinct from any astrological reading of the region of the summer Milky Way it occupies.
Aquila's other seventeenth-century neighbour besides Sagitta is Scutum, Sobieski's Shield, introduced by Johannes Hevelius in 1684 to honour his royal patron John III Sobieski of Poland, a rare surviving example of the patron-flattery constellations several astronomers of the period tried to establish, most of which, honouring other rulers and dynasties, failed to outlast their own century. The Ganymede myth attached to Aquila, the eagle sent to carry the beautiful youth up to Olympus to serve as cupbearer to the gods, is one of the few constellation stories in this catalogue with a homoerotic theme preserved openly in the classical sources rather than euphemised by later retellings.