Altair: The Flying Eagle

Altair is the 12th brightest star in the night sky and the brightest star in Aquila, the Eagle. As the southern vertex of the Summer Triangle, Altair has been one of the most important navigational and cultural stars for thousands of years. It is also one of the nearest bright stars to Earth and one of the fastest-rotating stars visible to the naked eye. Find it in the summer sky with StarGlobe.

How to Find Altair

Altair is the southernmost star of the Summer Triangle, below and between Vega (to the northwest) and Deneb (to the northeast). A distinctive feature helps confirm its identity: Altair is flanked closely by two fainter stars, Tarazed above and Alshain below, creating a compact line of three stars. This trio is easy to spot and sets Altair apart from other bright stars in the region.

The Milky Way runs between Altair and Vega, adding a dramatic backdrop to this part of the sky. From the Northern Hemisphere, Altair is well-placed during summer and autumn evenings, appearing in the south to southwest.

Physical Characteristics

Altair is a white main-sequence star of spectral type A7V, located only 16.7 light-years from Earth. It has about 1.8 times the Sun's mass and approximately 11 times its luminosity. Its surface temperature of about 7,670 Kelvin gives it a bright white appearance.

Altair's most remarkable physical property is its extraordinarily rapid rotation. The star completes a full rotation in just about 8.9 hours, compared to the Sun's roughly 25-day period. This extreme spin causes Altair to bulge significantly at its equator, making its equatorial diameter about 22% larger than its polar diameter. Interferometric imaging has directly confirmed this oblate shape, making Altair one of the first main-sequence stars to have its surface features directly resolved.

The rapid rotation also causes gravity darkening, where the equatorial regions are cooler and dimmer than the poles. This means Altair looks different depending on the viewing angle. From Earth, we see it at an intermediate inclination of about 57 degrees, so both effects are visible.

Altair in the Summer Triangle

The Summer Triangle connecting Altair, Vega, and Deneb is one of the largest and most prominent asterisms in the sky. Despite spanning constellations in three different regions, the triangle is so distinctive that it often serves as the first pattern newcomers learn in the summer sky. The three stars represent three different stages of stellar evolution: Vega is a mature main-sequence star, Altair is a younger main-sequence star, and Deneb is a supergiant nearing the end of its life.

Cultural Significance

Altair's name comes from the Arabic "an-nasr at-ta'ir," meaning "the flying eagle." In one of the most beloved astronomical legends, originating in Chinese mythology, Altair represents Niulang, the Cowherd, separated from his beloved Zhinv, the Weaver Girl (Vega), by the celestial river of the Milky Way. The two flanking stars, Tarazed and Alshain, represent the couple's children. They are reunited once a year when magpies form a bridge across the river, a story celebrated during the Qixi Festival (China) and Tanabata (Japan).

In Babylonian and Sumerian tradition, Altair was associated with the eagle, a symbolism that carried through to Greek and Roman astronomy. Aboriginal Australian cultures recognized Altair and its flanking stars as a distinctive group, incorporating them into their constellation systems. In some Polynesian navigation traditions, Altair's rising point on the horizon served as a directional guide.

Altair and Aquila

Aquila, the Eagle, is shaped like a broad cross or diamond with Altair at its center. The constellation lies along the Milky Way and contains several interesting objects, including the dark nebula Barnard's E (B142 and B143), two dark dust clouds visible in binoculars as dark patches against the bright Milky Way background. The constellation also contains several planetary nebulae and open clusters for telescope users.

Best Time to Observe

Altair is best observed from July through October, reaching its highest point during August and September evenings. The Summer Triangle, of which Altair is a member, remains visible from June through December for Northern Hemisphere observers. At its declination of about +9 degrees, Altair is visible from virtually all inhabited regions of Earth, making it a truly universal star.

From the Southern Hemisphere, Altair appears in the northern sky during southern spring and is well-placed for observation from July through November.

Neighboring Stars and Constellations

Vega in Lyra lies to the northwest, and Deneb in Cygnus is to the northeast. Sagittarius lies to the south, and Capricornus and Aquarius extend to the southeast. Scutum and Serpens Cauda sit to the southwest. Sagitta, the Arrow, and Vulpecula, the Fox, occupy the space between Altair and Deneb. Explore the heart of the Summer Triangle with StarGlobe.

Quick Facts

Altair has an apparent magnitude of 0.76, a distance of 16.7 light-years, and a luminosity about 11 times the Sun. Its rotation period is only 8.9 hours, causing significant equatorial bulging. Its mass is approximately 1.8 solar masses. Its right ascension is 19h 51m, and its declination is +8 degrees 52 minutes.