First, Altair rotates rapidly. This star requires only about 10 hours to spin once on its axis, in contrast to 24 hours for our Earth to spin or roughly a month for our sun. In other words, this mighty star spins on its axis more rapidly than Earth! This rapid rotation tends to flatten the star a bit, much as a pizza crust flattens as it spins. Estimates are roughly that Altair’s flattening is about 14 percent. The sun also is an oblate spheroid, although its flattening is difficult to measure due to the low rotation rate.
How to see it
Altair is the 12th brightest star, and so it is respectably bright (apparent magnitude 0.76 or 0.77), a fact that increases your likelihood of spotting it in summer or autumn skies. What’s more, Altair is flanked by two other stars, Tarazed and Alshain. When you see them, you might think of these stars as walking three abreast and arm-in-arm across the heavenly sphere.
Altair is also known as Alpha Aquilae, and it is the brightest star in the constellation Aquila the Eagle.
What’s more, stargazers know Altair as part of an entirely different and much-larger – but very recognizable – pattern. Altair is the southern apex of the Summer Triangle, which is also composed of the stars Vega and Deneb.
On the first of June, Altair rises about 90 minutes after sunset, as viewed from mid-north latitudes. By the end of September it approaches the meridian as night falls. By the end of the year, late-night observers will miss it altogether as it sets less than three hours after the sun.
Many depictions place Altair as the head or neck of an eagle with outstretched wings. The tips of the wings are formed by the Theta and Zeta stars of the constellation Aquila the Eagle, with the tail being Lambda. Once visualized, Aquila the Eagle can be seen flying eastward through the Milky Way, apparently about to devour the tiny constellation Delphinus, the Dolphin.
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