By late summer, Aquila the Eagle is high in the southern sky after dark, its brightest star blazing almost directly overhead from mid-northern latitudes. It's one of the three constellations that make up the Summer Triangle, and once you know where to look, it becomes one of the more satisfying star patterns to find -- clear in shape, rich in interesting stars, and sitting in one of the densest stretches of the Milky Way visible from the northern hemisphere.
Finding Aquila in the Sky
Aquila is easiest to find by starting with the Summer Triangle. The three stars of the triangle are Vega, Deneb, and Altair. Altair is the southernmost of the three -- the bright, slightly yellowish-white star low in the south compared to the others -- and it marks the neck of the Eagle. From Altair, two slightly fainter stars flank it closely on either side: Tarazed to the upper right and Alshain to the lower left. These three stars in a short diagonal line are unmistakable once you know them.
The body of the Eagle extends outward from Altair in a rough cross shape, with wings spreading to either side and a tail dipping southward. The Milky Way runs directly through the constellation, and sweeping through it with binoculars on a dark night reveals extraordinarily dense star fields -- this part of the sky looks toward the inner regions of the galaxy.
Aquila sits on the celestial equator, making it visible from virtually every location on Earth. It's best placed for viewing from July through October.
Altair -- One of Our Closest Neighbors
Altair is only 17 light years from Earth, which makes it one of the closest bright stars in the sky. That proximity is part of why it appears so prominent -- it's genuinely nearby by stellar standards, not just intrinsically brilliant.
What makes Altair truly unusual is its rotation. It spins once every nine hours, compared to the Sun's 25-day rotation period. That speed is so extreme that Altair is visibly flattened at the poles -- its equatorial diameter is about 20 percent wider than its polar diameter. In 2006, astronomers used an interferometer to directly resolve the disk of Altair and confirmed its oblate shape. It's one of only a handful of stars other than the Sun whose actual surface has been imaged.
From Earth, Altair looks like a steady white point of light. The reality is a rapidly spinning, visibly non-spherical star close enough to observe in unusual detail.
Tarazed and the Other Stars of the Eagle
Tarazed, the orange giant flanking Altair to the upper right, is a striking contrast in color and character. Where Altair is close and fast-spinning, Tarazed is a distant evolved giant -- about 460 light years away and roughly 100 times the diameter of the Sun. Its orange color is visible to the naked eye when you look at it next to Altair's white light, and together the three-star line of Tarazed, Altair, and Alshain is one of the more satisfying small asterisms in the summer sky.
Eta Aquilae, further into the constellation, is a Cepheid variable star -- a type of star that pulsates in brightness over a regular period. Eta Aquilae brightens and dims over a cycle of about 7.2 days, a variation subtle enough that it requires attention to detect but significant enough to have been studied for centuries. Cepheid variables are important to astronomers because the relationship between their pulsation period and their true luminosity allows them to be used as distance markers across the galaxy and beyond.
The Mythology of Aquila
In Greek mythology, the eagle in the sky is Zeus's bird -- his personal messenger and the carrier of his thunderbolts. In one version of the myth, it was the eagle that carried the young Ganymede up to Olympus to serve as cupbearer to the gods, and Aquila was placed in the sky to commemorate the act.
In another tradition, the eagle is connected to the story of Prometheus -- the Titan who stole fire from the gods and gave it to humanity. As punishment, Zeus had Prometheus chained to a rock where an eagle came each day to eat his liver, which regenerated overnight. The eagle of that story is sometimes identified with Aquila, though the constellation appears in ancient records far earlier than the myth was attached to it.
Aquila is one of Ptolemy's original 48 constellations, appearing in his 2nd century CE catalog, and it has been a continuous presence in Western star maps ever since.
What to Look For in Aquila
The densest part of the Milky Way visible from the northern hemisphere runs directly through Aquila and into Sagittarius and Scorpius to the south. On a genuinely dark night, the star clouds in this region are extraordinary -- dense and textured, with dark lanes of dust cutting through the brightness. Aquila sits at the northern edge of this richest region, and sweeping slowly through it with binoculars is one of the better experiences the summer sky offers.
NGC 6751, a small planetary nebula embedded in the constellation, is a remnant of a star that ended its life much as our Sun eventually will -- shedding its outer layers into an expanding shell of glowing gas. It requires a telescope to see clearly, but it's there in the same patch of sky you can take in with a glance overhead on a late summer night.
Name a real catalogued star in Aquila or any of our 30 curated constellations at NamedLight