Eagle in the Balance

• ‹ Previous program
• 617 of 1964
• Next program ›

Aquila is a large constellation, and most of its stars are faint, so it's hard to "see" the eagle that it depicts. In fact, in ages gone by, the entire eagle was often represented by just three stars: its brightest star, Altair, and two fainter stars that flank it. Altair was the eagle's body, while Alshain and Tarazed were its wings.

Tarazed is the brighter of the two. Its name is from a Persian phrase that means "the beam of the scale." Not only did skywatchers look at these stars as an eagle, they also saw them as a balance scale.

Tarazed is a stellar giant. It's about five times as massive as the Sun. Because of that great heft, it's aged much faster than the Sun. It's already entering the final stages of life, even though it's only a few percent as old as the Sun.

As part of that endgame, the star has puffed up -- it's about a hundred times wider than the Sun. Fairly soon, it'll cast its outer layers into space, leaving only its hot, dense core: a white dwarf -- an object as massive as the Sun, but no bigger than Earth.

The same fate awaits Alshain, but not for a long time. It's only a little heavier than the Sun, so it'll probably live billions of years longer. That'll leave the eagle with just one wing -- and the scales out of balance.

For now, though, look for this trio high in the southeast at nightfall. Altair is the southernmost point of the Summer Triangle. Tarazed is above it, with Alshain below.

Script by Damond Benningfield, Copyright 2009

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