The Eagle's Tail

• ‹ Previous program
• 256 of 1971
• Next program ›

The constellation Aquila is a skywatching rarity: a pattern of bright stars that really does resemble its namesake -- in this case, an eagle. It's not that hard to see two widespread wings and a graceful neck in the constellation.

But the people who drew the constellation may have gone a little too far with the eagle's tail feathers. They're way off center, behind Altair, the constellation's brightest star, which is near the northern wingtip.

Astronomers refer to the two "tail" stars as Zeta and Epsilon Aquilae. But together, they also have an older Arabic name: Deneb al Okab -- the eagle's tail.

The northern star in the tail is actually a system of three or more stars. Only one of them is bright enough to see with the unassisted eye. It's a type of star known as a red giant. That means it's in the final stages of life. Its core is getting hotter and denser, while its outer layers are puffing out and getting cooler. That's the same process that awaits the Sun in several billion years.

The southern star is a multiple-star system, too. Its brightest star is fairly early in life. It's bigger, heavier, and hotter than the Sun. And it spins like mad: close to 200 times faster than the Sun. That means the star bulges out at the equator, so it looks like a squished beachball.

Look for the eagle high in the southeast at nightfall, high above the gibbous Moon. It soars across the south in late evening, and sets before dawn.

Script by Damond Benningfield, Copyright 2005, 2008

For more skywatching tips, astronomy news, and much more, read StarDate magazine.