The great Summer Triangle will take you places
When you’re trying to make the stars your old friends and getting to know your way around the constellations you need all the help you can get. Asterisms can be wonderful tools to get the job done. Asterisms are large and obvious formations of stars that are very easy to find. They are not counted among the official constellations in the night sky, but they’re a heck of a lot easier to find because they’re all made up of bright stars and jump right out at you. They can be either part of a constellation or made up from several constellations.
One example of an asterism is the Big Dipper, now hanging by its handle in the northwestern sky. The Dipper makes up the rear end and tail of the constellation Ursa Major, the Latin name for the Big Bear. Its stars are by far the brightest members of Ursa Major and can be seen even in light polluted skies. The Big Dipper is the first step to seeing the rest of the Big Bear. It also acts as a nice pointer to other constellations. For instance, if you extend the curve or arc of the Big Dipper’s handle beyond the end of the handle with your mind’s eye you’ll run right into Arcturus, the brightest star in the summer evening sky, shining proudly in the high western sky. Arcturus is also the brightest star in the constellation Bootes the Hunting Farmer.
The best asterism of summer is aptly named the Summer Triangle, and it’s one of the biggest asterisms in the sky. Face yourself toward the evening eastern Marshall sky and look up for the three brightest stars you can see. That’s it! Those three stars are at the corners of the Summer Triangle. Each of the stars is the brightest in its own constellation, so straight away you have a way of locating three different constellations.
The brightest and highest star in the Summer Triangle is Vega. It’s the second brightest star in the summer evening sky and also an historic star. In the early ’80s it was discovered that Vega has a “dusty” ring around it, which was thought to be the start of a developing solar system. Vega with a planet system around it was featured in the movie “Contact” starring Jodie Foster.
Vega is 26 light-years away from Earth, with one light year equaling nearly 6 trillion miles. A light-year is defined as the distance light travels in a year’s time. That means the light we see from Vega tonight left that luminary when Bill Clinton was our President in 1993.
As bright as Vega is, it’s the brightest star in the puny little constellation Lyra the Lyre (pronounced liar, honestly!). A lyre is a type of small harp. I’m not sure how the constellation is supposed to look like a harp. Vega and a small parallelogram of fainter stars to the lower right it is all there to Lyra.
The next brightest star you see to the lower left of Vega is Deneb on the lower left corner of the Summer Triangle. Deneb is the brightest star in the constellation Cygnus the Swan. Within the swan is a small asterism called the Northern Cross, because it really looks like a sideways orientated cross with Deneb at the top of the cross. To make it into a swan, make Deneb the tail of the Swan and the star Albireo at the foot of the cross the head of the big heavenly bird. Then extend both ends of the crosspiece of the cross to make a curved wingspan and there you have Cygnus the Swan on the wing.
Deneb may be the faintest of the Summer Triangle stars, but that’s only because it’s so far, far away, to the tune of 1,500 light-years away! It’s actually a humongous star that could be over 175,000 million miles in diameter. Our own sun isn’t even a million miles in girth! The light we see from Deneb tonight left that star in 500 A.D., way before Twitter and Facebook.
By the way, the star Albireo at the foot of the Northern Cross, or the head of the Swan, is the best double star in the sky. Even with a small telescope the seemingly mundane star is revealed as a gorgeous colorful pair about 400 light-years away. One star is a pale orange and the other is a very distinct blue. Don’t miss it!
The star on the lower right hand corner of the Summer Triangle is Altair, the brightest star in the constellation Aquila the headless eagle. Altair and four other stars make up a large vertical diamond that outlines the wingspan of the eagle. Altair is the closest to us of the Summer Triangle stars at just a little over 16 light years away. What’s really unusual about Altair is that it rotates once on its axis in only 10 hours. It takes our sun about a month to accomplish the same thing. Because of that Altair is a lot wider at its equator than its poles. You can’t tell by looking at it, even with a large backyard telescope, but it looks like a star that really needs to go on a diet!
There you have it, the Summer Triangle. It covers a large chunk of the summer sky, and along with helping you find the three constellations within it you can also use it to easily find nearby constellations like Hercules the Hero, Draco the Dragon, Delphinus the Dolphin, and many more. Don’t go stargazing this time of year without it!
Mike Lynch is an amateur astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis/St. Paul. He is also the author of “Stars: a Month by Month Tour of the Constellations,” published by Adventure Publications and available at bookstores and at adventurepublications.net.