StarDate: August 18, 2009

You are missing some Flash content that should appear here! Perhaps your browser cannot display it, or maybe it did not initialize correctly.

audio/mpeg icon

One of the jewels of the summer sky is Vega, the brightest star in the small constellation Lyra, the harp. It's the fifth-brightest star in the entire night sky.

Vega's one of our nearest stellar neighbors -- just 25 light-years away. In other words, the light we see from Vega tonight actually began its journey toward Earth near the end of Ronald Reagan's first term as president.

Vega is a white star, which means that its surface is hotter than the Sun's. But Vega generates light the same way as the Sun: Nuclear reactions in its core convert hydrogen into helium.

While the Sun and Vega are similar in some ways, in one way they're quite different: They spin at very different speeds.

The Sun rotates just once a month. Vega, on the other hand, spins twice a day. In fact, if the star spun just a bit faster, it would fling itself apart. Because of that high-speed rotation, Vega bulges out at the equator. It's about 23 percent fatter at the equator than through the poles.

Here on Earth, we see Vega nearly pole-on. Because of that, it took astronomers awhile to measure Vega's thrill-ride rotation -- a rotation that gives the star a bulging waistline.

Vega is easy to pick out on any summer night. This week, it's high overhead as darkness falls, and low in the northwest at first light. It's so bright that it's visible from just about everywhere -- even from the light-polluted confines of places like New York City.

Script by Ken Croswell, Copyright 2009

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

The one constant in the Universe: StarDate magazine


©2014 The University of Texas McDonald Observatory