When itís finally dark enough for stargazing this time of year ó and thatís after 10 p.m. for decent stargazing ó thereís a sure sign of summer among the rising stars in the east-northeast. Itís the bright Summer Triangle, made up of the three brightest stars from three different constellations, each of the stars being the brightest in their respective constellations. Finding the Summer Triangle is easy. Just look for the three brightest stars you can see in the northeastern sky.
The highest and brightest star is Vega, a significant and even historic star. It is the brightest star in the tiny constellation Lyra the Lyre, which is supposed to be an old-fashioned harp. Vega is the third-brightest nighttime star we see during the course of the year. The main reason itís so bright is that itís relatively close. Itís only 25 light years away.
Vegaís diameter is believed to be a little over 2 million miles across, about 2.5 times our sunís diameter. Itís also twice the mass of our sun. Astronomers have concluded that Vega is only about a tenth of the sunís age and thatís part of the historical aspect of this young star. Astronomers have detected at least one planet about the size of Jupiter orbiting Vega.
The second-brightest star in the Summer Triangle is Altair, on the lower right hand corner. Itís the brightest star in the constellation Aquila the Eagle. Altair is even closer to Earth than Vega at just under 17 light years away. The remarkable thing about Altair is that itís a real spinner, rotating on its axis once every nine hours. By comparison, it takes our sun about a month to make a complete spin. Itís whirling so fast that Altair is lopsided. Itís believed that its equatorial diameter is at least 20 percent larger than its polar diameter. Many astronomers believe that if Altair spun much faster it would literally fly apart. Now thereís no way you can see Altair as a lopsided star through even the largest of backyard telescopes, so you donít have to worry about getting dizzy gazing at it.
The third and faintest star in the summer triangle is Deneb, on the lower left corner. Itís the brightest star in the constellation Cygnus the Swan. Cygnus also has the nickname ďThe Northern CrossĒ because it really looks like a cross. Deneb is positioned at the top of the cross, which is rising on its side above the eastern horizon. Just gaze to the right of Deneb and youíll see the crosspiece and the rest of the cross.
Even though Deneb is the faintest star in the Summer Triangle, itís one of the largest and most luminous stars in our part of the Milky Way galaxy. Itís believed to be 200 times the size of our sun and kicking out around 60,000 times the light. If you were to put Deneb in place of our sun, the inner planets Venus and Mercury would be living inside Deneb, and whatís left of our Earth would be at the outer edge of the great shiner.
Enjoy the Summer Triangle, not only this summer, but into this autumn as it gradually migrates to the west from night to night.
Mike Lynch is an amateur astronomer and professional broadcast meteorologist.
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