Jimmy Westlake: Summer’s Triangle
June 8, 2008
There are few sights in nature any more beautiful than the starry summer sky. When the sun goes down and the summer stars come out, three of the first ones you see high in the northeastern sky will be the trio of bright stars that forms the corners of an unmistakable asterism called the Summer Triangle. Although it is called the Summer Triangle, it first becomes visible during the early evening in late spring and hangs on in our evening sky until early winter.
Asterisms are dot-to-dot drawings in the sky that are widely known but are not counted among the 88 official constellations. The Big Dipper is another example of an asterism. In many cases, asterisms are easier to recognize than the official star patterns. The Summer Triangle is a case in point.
The brightest star in the Summer Triangle and the first to rise is Vega, named for “the plunging vulture.” At a distance of only 25 light years, Vega is among the closest stars to our solar system. Vega became a real “movie star” in 1997 when astronomer Carl Sagan chose it as the source of the first extraterrestrial signal detected by radio astronomers on Earth in his fictional book and movie “Contact.” In real life, Vega was one of the first stars discovered to have a ring of planetary material surrounding it, possibly a family of planets in the process of formation.
The second star to rise in the Summer Triangle is its faintest member, the blue supergiant star named Deneb, meaning “the tail of the swan.” Although Deneb shines nearly as bright as Vega, it does so from a distance of 1500 light years away. If Deneb were moved into the same distance from Earth as Vega, it would shine more than 1,700 times brighter than Vega and cast distinct shadows at night. Deneb is one of the most luminous stars known to astronomers.
Finally, the third member of the Summer Triangle, marking its southern-most corner, is the star named Altair, which means “the flying eagle.” Altair is the closest of the three stars in the Summer Triangle, lying at a distance of only 17 light years. Each of the stars in the Summer Triangle falls in a different constellation: Vega is the brightest star in Lyra the Harp, Deneb belongs to Cygnus the Swan, and Altair is the Alpha star of Aquila the Eagle. You can use the Summer Triangle asterism as a guide to locate many other official constellations of summer.