Summer Triangle of stars still visible
The first day of fall has come and gone. The nights are now longer than the days, the leaves are changing, and it's gradually getting cooler. Summer is over, although we can still get those warm sunny days — what's often called Indian Summer.
The evening sky still has a lot of summer in it. In fact, constellations are a lot like major league sports, as there's a lot of overlapping of seasons.
While the autumn constellations like Andromeda, Pegasus, Aries and others are lighting up our eastern evening skies, there are still many summer constellations stretched across the western half of the heavens.
Eventually the Earth, in its obedient orbit around the sun, will turn completely away from the stars of summer — but for now, they're making their last celestial shine for this year.
As a matter of fact, after sunset this month, look overhead for the three brightest stars you can see. Those stars make up something called the "Summer Triangle." Each of those bright shiners is the brightest star in three respective summer constellations and each of them is very special in their own way.
The brightest of them is Vega, the brightest star in a small constellation called Lyra the Lyre, which is an old-fashioned harp. Vega is a star that's more than 25 light years away, with just one light year equaling nearly six trillion miles.
The light we see from Vega this week left that star when Ronald Reagan was just starting his presidency. Vega is also bigger and hotter than our sun. It's about 3 million miles in diameter, more than three times the girth of the sun and 17,000 degrees F at its surface, 7,000 degrees hotter than our sun.
In fact, you can tell Vega is one of the hotter stars in the sky by the faint blue tinge it shines with. The most significant fact about Vega, though, is that it marks the spot in space that our sun, Earth and the rest of the solar system are racing toward at over 12 miles per second!
The second brightest star in the Summer Triangle is Altair, the brightest star in constellation Aquila the Eagle. Altair is the closest star in the triangle, just over 16 light years away.
Now even with the best of backyard telescopes, there's nothing all that special you can see. However, astronomers know from spectroscopic analysis that Altair really has a spin to it, literally. It rotates on its axis every 10 hours! It takes our sun nearly a month to make a complete spin.
In fact, Altair spins on its axis so fast that it's believed to be a lot fatter at its equator than it is at its poles. Because of centrifugal force, it's actually an oval-ish star.
My favorite star in the Summer Triangle is the faintest. Deneb, the brightest star in the constellation Cygnus the Swan, also known as the Northern Cross, is one fanatically large and luminous star.
According to the latest data, this star at the tail of the heavenly swan is more than 3,200 light years away. As well as we see this star, you have to figure that it's one humongous star. In fact, it may be more than 250 million miles in diameter and kicking out more than 39,000 times more light than our sun.
If you could magically pull Deneb in from 3,000 light years away to the distance of Vega, about 25 light years away, about the only thing brighter in the sky would be the moon!
Deneb is virtually the biggest single thing you can see with the naked eye in our October skies!
Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis and author of the book, "Pennsylvania Starwatch," available at bookstores and at his Web site www.lynchandthestars.com.
