Summer Skies Don’t End at Labor Day

by Rod Kennedy

Labor Day is typically regarded as the unofficial end of summer. School starts, swimming pools close, football season stars, and baseball teams start their end of season race to the pennant. For night sky observers, September begins the fall observing season; a time when the sun sets earlier, and the skies are clear and steady. It may be ironic then, that one of the brightest groups of stars visible in the September sky is an asterism known as the Summer Triangle. This asterism, and the constellations that make it up, are full of good targets for observing on September nights.

Despite its name, the Summer Triangle, it is almost directly overhead during September. The three brightest stars of the Summer Triangle are Vega, Altair and Deneb. Each of these stars is the brightest star in a constellation of its own. Vega is the brightest star in the constellation Lyra the Harp. Altair is the brightest star in Aquila the Eagle, and Deneb is the brightest star in Cygnus the Swan. Each of these stars is clearly visible to the naked eye even under light polluted skies. Observers wanting to dig a little deeper into these constellations will want to travel to darker skies and take a small telescope.

Looking to Lyra the Harp we find a variety of interesting objects. The most famous is M57, the Ring Nebula. If we visualize Lyra as a parallelogram, Vega is an extension of the left hand side. The two stars on the opposite side are Sheliak and Sulafat. The Ring Nebula lies almost equidistant between these two stars. The Ring Nebula is the puffed off remains of a star that was once like our own sun. As it ran out of fuel its outer layers expanded out into space, rather like an expanding soap bubble. On the same side of the parallelogram as Vega are the stars Delta Lyrae and Zeta Lyrae. Zeta Lyrae is the upper star, closest to Vega. Looking at Delta Lyrae with a telescope reveals it to be a beautiful little open star cluster.

Cygnus the Swan is extremely rich in deep sky objects since it lies along the Milky Way. Deneb represents the tail of the swan, while the star Alberio represents the swan’s bill. Alberio is very interesting through a telescope. Under low magnification Alberio reveals itself to be a binary star system, two stars orbiting each other. The two stars of the Alberio system are interesting because they are different colors. One is a deep gold color, while the companion is a bright blue. This means the stars are different temperatures, with the blue one being hotter. Near the heart of Cygunus is M29, another open cluster containing more than a dozen stars.

Of the three constellations of the Summer Triangle, Aquila the Eagle is the least dense in interesting objects. The best object is M11, located about half way between the bright star Altair and the top of the Teapot asterism (Sagittarius). M11 is a beautiful maze of stars at a distance of nearly 6,000 light years away.

For many people, September is the start of fall; and as the Fall Equinox occurs in September this is a fairly accurate assumption. However, even though the temperature may cool, the days shorten and the leaves turn to gold, the stars of summer linger in the night sky for much longer. The bright stars of the Summer Triangle hang around until many of us feel the approach of winter.

September 2012 Chart

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