Driftless Dark Skies: Summer Triangle

July 6th, 2016 by John Heasley

As darkness falls this month, watch for three shining stars emerging in the east.   They are the brightest stars in three separate constellations, but together they form an asterism (a star pattern) known as the Summer Triangle.  They cover an area of sky larger than your outstretched hand. 

Milkyway_Swan_PanoramaVega is the highest of the three and is the main star of the constellation Lyra the Lyre.  The light you see left Vega back in the spring of 1991.  Below and to the right of Vega is Altair in the constellation Aquila the Eagle.  It is closer to Earth, and its light has been journeying since the fall of 1999.  As the sky darkens, watch for our home galaxy, the Milky Way, passing between the two stars. 

There is a story of the two stars told in Japan, China, and Korea.  Altair, a poor herdsman, falls in love with Vega, a princess.  Vega’s father places them on opposite sides of the heavenly river, the Milky Way.  Once a year on the seventh day of the seventh month, the Emperor shows mercy and Altair is allowed to cross the river to visit with Vega. 

The third star of the Summer Triangle is Deneb.  Look for it between and to the left of Vega and Altair.  Deneb is the tail of Cygnus the Swan.  You can make out the outstretched wings of the Swan just to the right of Deneb reaching up and down.  Its long neck reaches almost as far as a line traced between Vega and Altair.  I imagine Cygnus as flying over the Milky Way.  Deneb is one of the farthest and most luminous stars you can see with your naked eyes.   It is over 200 times larger and 250,000 times brighter than our Sun.  The light you see left Deneb at least 1425 years ago. 

There are three planets to go along with the three stars.  Jupiter is bright in the southwest as night falls.  The Waxing Crescent Moon passes by Jupiter on July 8 and 9.  Mars and Saturn are glowing in the south just above Scorpius the Scorpion.  The Waxing Gibbous Moon passes by Mars on July 14 and by Saturn on July 15.  Just below Saturn, look for Antares whose name means “rival of Mars”. 

You will have a chance to see these stars and planets through a telescope when Starsplitters have a public program at Wyalusing State Park on July 9 (8:30pm) and Northwest Suburban Astronomers have a public program at Wildcat Mountain State Park on July 30 (8:00pm).  Or just enjoy the sight of the three stars and three planets coming out in the dark skies over the Driftless Area. 

John Heasley is an astronomy educator and stargazer who enjoys connecting people with the cosmos. He volunteers with NASA/JPL as a Solar System Ambassador. For more information about stargazing in southwest WI, like Driftless Stargazing LLC on Facebook and find out whenever there’s something awesome happening in the skies. Driftless Dark Skies appears monthly in the Voice of the River Valley.

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