View the 'Summer Triangle' and Its Bright Stars This Week

By Joe Rao, Space.com Skywatching Columnist | August 28, 2017 12:00pm ET

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The famous "Summer Triangle" will appear overhead around 9:30 p.m. local time this week. The summer sky landmark is not a constellation itself, but rather three bright stars from three separate constellations. The pattern is nearly isosceles, which means it appears as a triangle with two equal-length sides.

Brightest of the three is the bluish-white Vega, in the constellation of Lyra, the Lyre. Next in brightness is the yellowish-white Altair in Aquila, the Eagle. Finally, there is white Deneb in Cygnus, the Swan. To our eyes, Vega appears twice as bright as Altair and more than three times brighter than Deneb. 

Apparent brightness can be deceiving, however, and regarding actual luminosity a different tale is told: brilliant Vega is 40 times brighter than our sun and 25 light-years away. Altair is 10 times brighter than the sun and is one of our nearer neighbors at just 17 light years away; it owes its splendor in the summer skies to its nearness to the Earth. But Deneb is one of the greatest supergiant stars known. Its luminosity is nearly 200,000 times that of the sun, yet at 2,600 light-years away it appears to us as a fairly conspicuous but by no means particularly notable star. But if it were somehow possible to move Deneb to Vega's distance from us, it would then appear to shine some 40 times brighter than Venus, capable of casting distinct shadows and even being visible in the daytime.[Morning Milky Way Shines Over Summer Triangle in Stunning Photo]
 
A special treat of the Summer Triangle's noticeable prominence in summer months is the visible framing of the Milky Way between Vega and Altair. Deneb appears to lie in the middle of the Milky Way's dim band. 

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