The official first day of summer isn’t until June 20, but already, there’s a sure stellar sign of summer on the rise. When the night sky finally darkens around 10:30, the “Summer Triangle” emerges in the eastern sky. Unlike the 65 to 70 official constellations we can see around here, the Summer Triangle is an “asterism,” a distinct pattern or picture in the stars that isn’t an official constellation. Most asterisms are composed of bright stars from various constellations, and the Summer Triangle is no exception. It’s a sight that can be enjoyed even from a brightly lit urban area, making it accessible to all. Simply look for the three brightest stars in the low to mid-eastern sky, and you’ve found it. Each of these stars is the brightest in their respective constellations and has unique characteristics.
The most brilliant and highest star in the Summer Triangle is Vega. No, it’s not named after the car Vega, one of the 1970s rollouts from Chevrolet that had a very brief run. Vega is an Arabic name that roughly translates in English as “falling or swooping.” That definition certainly doesn’t apply to Vega, at least not at this time of the year, as it rises in the evening. Vega is the brightest star in a small constellation called Lyra the Lyre, an old-fashioned harp. Vega is over 25 light-years away, with just one light-year equaling nearly 6 trillion miles. The light we see from Vega this week left that star when Beanie Babies were wildly popular in the late ’90s. Vega is about 2 million miles in diameter and 17,000 degrees Fahrenheit. at its surface, more than twice the diameter and 7,000 degrees hotter than our sun. You can tell that Vega is one of the hotter stars in the sky by the faint blue tinge it shines with.
The second-brightest star in the Summer Triangle is Altair, located in the lower right corner of the eastern sky. Altair, the brightest star in the Aquila constellation, is the closest star in the triangle, just over 16 light-years away. Despite its proximity, even the best backyard telescopes won’t reveal anything special about Altair. However, astronomers have discovered that Altair has a fast spin through spectroscopic analysis. It completes a full rotation on its axis every 10 hours, compared to our sun’s monthlong rotation. This rapid spin causes Altair to be much fatter at its equator than at its poles, giving it an oval shape. It’s a star with a beer belly!
My favorite star in the Summer Triangle is the faintest member in the left-hand corner. It’s Deneb, the brightest star in the constellation Cygnus the Swan, also known as the Northern Cross. Deneb is one incredibly large and luminous star. According to the latest data, this star at the tail of the heavenly swan is at least 1,500 light years away but very possibly much farther! As bright as Deneb is, considering its vast distance, it’s easy to conclude that it’s enormous. In fact, it may be over 200 million miles in diameter and emitting at least 55,000 times more light than our sun, but probably much more. If you could magically pull Deneb in from its 1,500 light-year distance to the proximity of Vega, about 25 light-years away, the only thing that would be brighter in the sky would be the full moon! Deneb is one of the biggest single things you can see with the naked eye in our early summer skies!
Mike Lynch is an amateur astronomer and retired broadcast meteorologist for WCCO Radio in Minneapolis/St. Paul. He is the author of “Stars: a Month by Month Tour of the Constellations,” published by Adventure Publications and available at bookstores and adventurepublications.net. Mike is available for private star parties. You can contact him at mikewlynch@comcast.net.
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