Gaze at the night sky enough, and you’ll begin to find all kinds of geometric patterns among the stars.
Points are easy; so are lines connecting two stars. Another easy pattern is a triangle, since any three stars form a triangle.
But there is one stellar triangle that’s so special that it has its own name: the Summer Triangle, outlined by three bright stars that shine low in the eastern sky after dark right now.
Let’s take a look at each of its three stars in turn.
The brightest of the stellar trio — and highest in the sky this week — is Vega (VEE-guh), the main star of the tiny constellation of Lyra, the harp.
This brilliant white star is one of the nearest to Earth, lying “only” 150 trillion miles from us. That means its light takes about 25 years to reach us (we say it’s 25 “light years” away).
So, when you view this star, keep in mind that the light you see departed Vega in the year 2000. In other words, you’re seeing the star as it was 25 years in the past.
Vega is about 2½ times larger and shines some 50 times more brilliantly than our sun.
And, because it burns so rapidly, astronomers believe that Vega will probably exhaust its fuel 10 times faster than our sun, making its expected lifespan only about 1 billion years.
Now check out the south-easternmost of the three stars. Altair (AL-tare) is the brightest in the constellation of Aquila, the eagle.
It appears much fainter than Vega, so one might conclude it’s farther away.
And this would be true if all stars were identical, but they’re not. In fact, Altair is closer than Vega, at a distance of only 17 light years.
Not only is Altair one of the nearest stars in our sky, but it’s also one of the most rapidly rotating.
Astronomers have found that this white star spins once every 6½ hours, completing nearly four rotations for every one made by the Earth.
Because of this rapid spin, astronomers think that centrifugal force may compress Altair so much that it might be shaped more like an egg than a sphere.
The third star in the Summer Triangle is Deneb (DEH-nehb).
You’ll probably notice that it appears similar in brightness to Altair, so stargazers might conclude that it must be the same distance.
Of course, you won’t make that mistake, because you know that stars all have different sizes and luminosities.
And there’s no better example of this than a comparison of Deneb and Altair.
While Altair is one of the nearest stars to us, Deneb is one of the farthest visible to the unaided eye.
It’s tough to measure its distance, but astronomers estimate that Deneb lies between 1,400 and 2,600 light years from us.
So why does it appear similar to one of the nearest stars in the sky? Because this blue supergiant is one of the most luminous in our galaxy, pumping out as much energy as 200,000 suns.
With summer nights approaching, I hope you’ll get out under the stars to explore this marvelous Summer Triangle.
