Asterisms can be wonderful tools to help you find your way around the constellations.
Asterisms are large and obvious formations of stars that are very easy to find. They are not counted as one of the official 88 constellations, but they’re a heck of a lot easier to find because they’re all made up of bright stars.
They can be either part of a constellation or made up from several constellations.
One example of an asterism is the Big Dipper, which 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 be seen even in the most light-polluted skies.
The Big Dipper is the first step to outlining the rest of the Big Bear. It can also act as a nice pointer to other constellations. If you extend the curve or arc of the Big Dipper’s handle beyond the end of the handle you’ll run right into Arcturus, the brightest star the brightest star in the constellation Bootes the Hunting Farmer.
The asterism I want to feature this week is the Summer Triangle, one of the biggest asterisms in the sky. Even though it’s officially autumn the Summer Triangle still has legs, and it’s very easy to find.
About 8 p.m. look overhead in the southern sky for the three brightest stars you can see. Those three stars are at the corners of the Summer Triangle. Each of the stars is the brightest in its own constellation, so you have a way of locating three different constellations.
The brightest star in the Summer Triangle is Vega on the upper right-hand side of the triangle, assuming you’re still facing south. It’s also the second brightest star in the summer evening sky and a historic star.
Currently Vega is about 26 light-years from Earth, with one light-year equaling nearly 6 trillion miles.
As bright as Vega is, it’s the brightest star in the puny little constellation Lyra the Lyre. 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 are all there really is.
If you’re still facing south, the highest star on the upper left-hand corner of the Summer Triangle is Deneb, 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 diagonally orientated cross with Deneb at the top. To make it into a swan, make Deneb the tail of the swan and the star Albireo at the foot of the cross is the head.
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 toward the southwestern horizon.
Deneb may be the faintest of the Summer Triangle stars but that’s because it’s so far, far away: 1,500 light-years. It’s actually a humongous star that could be more than 175,000 million miles in diameter.
Mike Lynch is an astronomer and professional broadcast meteorologist for WCCO Radio in Minneapolis and is author of the book, “Washington Starwatch,” available at bookstores. Check his website, www.lynchandthestars.com.
The Everett Astronomical Society: www.everettastro.org/.