Aquila, the Eagle, is a prominent constellation near the celestial equator, best known for its brilliant star Altair. Together with Vega in Lyra and Deneb in Cygnus, Altair forms the famous Summer Triangle, one of the easiest star patterns to recognize in the night sky.
Aquila is the 22nd-largest of the 88 recognized constellations, covering approximately 652 square degrees. Its position along the Milky Way makes it especially rewarding for observers interested in rich star fields, open clusters, and planetary nebulae.
Where and When to Find Aquila
Aquila is best observed from the Northern Hemisphere during July, August, and September, when Altair is prominent in the evening sky. The constellation can also be seen from much of the Southern Hemisphere.
The easiest way to locate Aquila is to find the Summer Triangle, formed by Vega, Deneb, and Altair. Altair is the southernmost of the three stars. Once you have identified Altair, look for two fainter stars on either side of it: Tarazed (Gamma Aquilae) and Alshain (Beta Aquilae). These three stars form a distinctive short line that helps identify the Eagle’s head and neck. From there, the constellation extends southward through a series of fainter stars toward the Milky Way’s rich star fields.
Aquila borders several constellations, including Cygnus, Sagitta, Scutum, Sagittarius, and Delphinus.
Aquila and the Summer Triangle
Altair is one of the three bright stars forming the Summer Triangle, alongside Vega in Lyra and Deneb in Cygnus. Unlike Aquila, Lyra, and Cygnus, the Summer Triangle is an asterism rather than an official constellation. Its three stars form a large, easily recognized pattern spanning a substantial region of the summer sky.
Altair is particularly useful for identifying the southern part of the triangle. From Vega, look southeast toward Altair; Deneb lies farther north, completing the pattern. The Milky Way passes through Aquila and Cygnus, making the Summer Triangle an excellent starting point for exploring the Galaxy with binoculars.
Mythology
In Greek mythology, Aquila represents the eagle of Zeus, the king of the gods. The bird was said to carry Zeus’s thunderbolts and serve as his messenger. In another well-known story, Zeus sent the eagle to carry Ganymede, a young Trojan prince, to Mount Olympus, where he became cupbearer to the gods. Ganymede is traditionally associated with the neighboring constellation Aquarius. Aquila was among the 48 constellations recorded by the Greek astronomer Ptolemy in the second century AD.
Notable Stars
- Altair (Alpha Aquilae) is the brightest star in Aquila and the 12th-brightest star in the night sky, shining at magnitude +0.77. Located approximately 16.7 light-years away, it is a white main-sequence star about 1.8 times the Sun’s mass. Altair rotates exceptionally quickly, completing a rotation in roughly nine hours. This rapid spin makes it noticeably flattened at the poles and wider around its equator. Its name derives from an Arabic expression meaning “the flying eagle.” Read more about Altair.
- Tarazed (Gamma Aquilae) is an orange giant shining at magnitude +2.7, located approximately 460 light-years away. It lies just northwest of Altair and is one of the two fainter stars that flank it in the sky.
- Alshain (Beta Aquilae) is a yellow-white subgiant approximately 45 light-years away, shining at magnitude +3.7. It lies on the opposite side of Altair from Tarazed, completing the easily recognized three-star pattern.
- Deneb el Okab (Zeta Aquilae) is a white main-sequence star approximately 83 light-years away, shining at magnitude +3.0. Its traditional name refers to the Eagle’s tail, and it helps trace the constellation’s larger outline.
- R Aquilae is a long-period variable red giant whose brightness changes dramatically as the star expands and contracts. It belongs to the Mira class of variable stars and can sometimes become bright enough to see with binoculars.
Notable Deep-Sky Objects
Although Aquila contains no Messier objects, its position along the Milky Way gives it a rich selection of star clusters and planetary nebulae.
- NGC 6709 is an open cluster approximately 3,500 light-years away, containing hundreds of stars. It lies about five degrees southwest of Deneb el Okab (Zeta Aquilae). With an apparent magnitude of around +6.7, the cluster is accessible through binoculars under favorable conditions, although a small telescope provides a better view of its scattered stars.
Image Credit: ESA / Hubble / NASA NGC 6741, also known as the Phantom Streak Nebula, is a compact planetary nebula approximately 7,000 light-years away. Despite its name, a planetary nebula has nothing to do with planets. It forms when an aging star expels its outer layers, leaving behind a hot stellar core whose radiation illuminates the surrounding gas. NGC 6741 is small and relatively faint, making it a challenging target for amateur telescopes.
- NGC 6751, sometimes called the Glowing Eye Nebula, is another planetary nebula in Aquila. Photographs reveal a striking circular structure surrounding its central star, with intricate filaments and knots of glowing gas. It is an attractive astrophotography target, although its faintness makes detailed visual observation difficult.
- NGC 6781 is a planetary nebula with a broad, roughly circular appearance. It is sometimes compared to the Ring Nebula in Lyra, although it is fainter and more challenging to observe. Aquila also contains the open cluster NGC 6755 and several other faint nebulae scattered across its rich Milky Way star fields.