Explore a Celestial Triangle

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Finding Beauty High in the Sky

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The Summer Triangle and the constellations that lend their stars to it. Carolyn Collins Petersen

Our skies are filled with stars that seem scattered into random groupings called constellations. Not every star pattern in the sky is a constellation, however. Sometimes, collections of stars from different constellations grab a stargazer's attention. That's the case with the Summer Triangle. It's visible through most of the summer and well into late autumn, making it a bit of a misnomer. However, it's high overhead in the late evenings of July and August, and that makes it a perfect summertime target for northern hemisphere stargazers.

The triangle is made up of the brightest stars of the constellations Lyra the Harp, Cygnus the Swan, and Aquila the Eagle. Those stars are called Vega, Deneb, and Lyra, respectively. Let's explore them!

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Begin with Lyra

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The constellation Lyra is a parallelogram-shaped star pattern, plus Vega at the top. Carolyn Collins Petersen

We'll start with Lyra. It's shaped like a parallelogram of stars with the brightest one, blue-white Vega, sticking out from the top. The ancient Greeks saw this pattern as the stringed instrument called a lyre. Vega, its brightest star and one corner of the Summer Triangle, is known formally to astronomers as alpha Lyrae. Because it's so bright, Vega has been known to stargazers throughout human history. Its name is a variant on the Arabic word "wāqi", for "falling or swooping eagle". Later cultures named it Wega and from that we get the name Vega. About 12,000 years ago, Vega was our pole star (much as Polaris is now), and in another 13,800 years, it will be our north star again.

If you have access to a good telescope and a dark-sky site, explore the region between the bottom two stars in the parallelogram. You might just be able to spot a dusty ring of light. It's the Ring Nebula, (an example of a planetary nebula) the remains of a star like the Sun that is in its final stages of death. 

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Visiting Vega

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Vega and its dust disk, as seen by Spitzer Space Telescope. The disk glows in infrared light because it is warmed by its star. NASA/Spitzer/CalTech

Vega lies fairly close to the Sun, at a distance of 25 light-years. At an estimated age of about 400 million years, it's much younger than the Sun, but is twice as massive as our star. If it evolves as massive stars usually do, Vega will last perhaps a billion years before it Astronomers have found a disk of dusty debris around Vega, and it is possible that Vega has a planetary system still forming around it. The debris probably comes from collisions of dwarf-planet type worlds in orbit around the star. 

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Cygnus Glides Down the Milky Way

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The constellation Cygnus with Deneb at the tail of the swan (top) and Albireo (the double star) at the nose of the swan (bottom). Carolyn Collins Petersen

The next constellation whose bright star is part of the Summer Triangle is Cygnus the Swan. It actually looks like a swan, and some people also see a oattern called the Northern Cross in the long body and wings. Cygnus is flying down the plane of the Milky Way (which is the faint band of light you can see running across the sky on summer and autumn nights) It's how our galaxy looks to us from the inside.

Cygnus has tantalized sky observers for centuries and was one of the 48 constellations charted out by the Egyptian-Roman astronomer Claudius Ptolemy in the second century CE. The Greeks saw this pattern in several of their myths, always connected to the idea of flight. Cygnus is visible from far southern climes, and so various Pacific Islanders gave it special names, too. 

Cygnus is filled with star clusters and nebulae (clouds of gas and dust) to explore. For some of them, you will need binoculars or a telescope. The brightest star (and the second corner of the Summer Triangle) is called Deneb, which is the tail of the swan. Astronomers list it as alpha Cygni. It's a bluish white-colored supergiant star about 200 times brighter than the Sun and 20 times more massive. It lies about 3,200 light-years from us. Astronomers think that Deneb will probably explode as a supernova in a few million years, and it will be the brightest star in the night sky.

As you explore Cygnus look at the star at the tip of the Swan's nose. It's called Albireo, and if you look at it through binoculars or a small telescope, you'll spot a lovely pair of stars: one blue and one gold.

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Soaring with Aquila, the Eagle

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The constellation Aquila and its bright star Altair. Carolyn Collins Petersen

The third constellation with a bright star in the Summer Triangle is Aquila, the Eagle. Its name is the Latin word for "eagle", and this star pattern has been well-known to observers since antiquity. There's evidence that this pattern was first charted by the ancient Babylonians, and its existence was subsequently shared with subsequent Greek and Roman cultures. 

The brightest star in Aquila (and the third point of the Summer Triangle) is brilliantly white Altair, more formally known as alpha Aquilae. Its name comes from the ancient Arabic term Al Nesr Al Tair (the flying Eagle). This star lies some 17 light-years from the Sun, is about twice the Sun's mass and shines 11 times more brightly than our star. It's an interesting star to astronomers because it rotates very rapidly — once every 9 hours. By contrast, our Sun rotates once every 25 days at the equator and once every 36 days at the poles. Altair's fast rotation means that this star is somewhat flattened, and astronomers have measured a difference between the temperatures at its poles and at its equator. 

Take some time to explore the area of the summer Triangle. Start with these bright stars and work your way across the sky to find some wondrous sites! 

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Petersen, Carolyn Collins. "Explore a Celestial Triangle." ThoughtCo, Aug. 23, 2016, thoughtco.com/explore-a-celestial-triangle-3072155. Petersen, Carolyn Collins. (2016, August 23). Explore a Celestial Triangle. Retrieved from https://www.thoughtco.com/explore-a-celestial-triangle-3072155 Petersen, Carolyn Collins. "Explore a Celestial Triangle." ThoughtCo. https://www.thoughtco.com/explore-a-celestial-triangle-3072155 (accessed October 24, 2017).