SkyCaramba weekly astronomy blog for the week ending May 28, 2011
The “second most important star in the sky” is up all night this time of year. Vega has been described that way because it’s so close and bright and easy to study.
Vega’s magnitude, the number representing its brightness, is almost exactly zero. It used to be exactly zero because it was the star astronomers used to calibrate their brightness measuring equipment. Today’s equipment is calibrated using methods that don’t require Vega to be in the sky.
In 1850, Vega was the first night sky star to be photographed. It seems nobody knows what happened to the picture. It probably didn’t survive. Pictures from that era were made of glass and required a lot of careful handling. Look up daguerreotype if you want to know more.
In 1872, Vega was a first photographic subject again when astronomers learned how to examine stellar spectra. The spectrum is what you see when you look at a light beam bent apart by a prism. By determining the colors in which the star shines brightest or dimmest, a scientist can tell what the star’s made of.
About 10,000 years ago, Vega was the northern pole star. It will be again in about 12,000 years. Stars shift around like that in our night sky because the earth is in a long slow wobble as it goes around the sun.
Astronomers believe Vega is a fast rotating star, bulging at the middle, with one of its poles pointed toward us. It’s rotating almost as fast as it can without flinging apart.
The star is one of our closest stellar neighbors, just 25 light years away. That’s close enough to easily measure its distance using the parallax method. That’s a comparison of the slightly different positions things appear to be in when viewed from different places. Over six months’ time, the earth moves from one side of the sun to the other and positions of the nearer stars seem to shift slightly.
You’ll find Vega in the constellation Lyra. It’s a parallelogram with a couple stars nearby. It looks like a clapper board used in film making (the thing someone holds in front of a camera and makes a clapping noise with when the director yells Action!).
Some of the oldest stories about it say this constellation is a vulture and Vega is the Vulture Star. To the Greeks, it was a harp, sometimes still held in a vulture’s claws or an eagle’s wings. Apollo gave this harp to his son Orpheus who played so well he almost charmed the gods into letting his dead wife out of Hades.
In Asia, Vega represents a princess who falls in love with a shepherd represented by the star Altair. They’re on opposite sides of the Milky Way stream because when they’re together they don’t get their work done. The lovers are said to rendezvous just one night every year.
I’ll tell you more about Altair another time. It and Vega are part of something called the Summer Triangle.