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Astronomy: Inside the Summer Triangle

8-19-11 M27 Chumack
The Dumbbell Nebula, M27, is part of the constellation Vulpecula. Credit: John Chumack

While it’s still summer and the Summer Triangle is easy to find, it’s a good time to explore what lies within its three walls. Look straight overhead to find the brightest star near the zenith on these nights — Vega — and to the south is Altair and the northeast is Deneb, the other two corners of the triangle. Deneb’s home constellation, Cygnus the Swan, lies within a large part of the Summer Triangle. But two small constellations, Vulpecula the Fox and Sagitta the Arrow, can also be found huddled near Altair.

Near the middle of the Summer Triangle is the head of the Swan, a star named Albireo. This double star appears readily through a telescope as a bright yellow member and a slightly dimmer blue star.

A couple weeks ago we talked about Vega’s constellation, Lyra, and the Ring Nebula that resides there. If you were to draw a line from the Ring Nebula to Albireo and then continue it toward the horizon, you would run across Vulpecula and then into another large nebula known as the Dumbbell Nebula, M27. The brightest portion of the Dumbbell Nebula has a rectangular shape with the two ends looking heavier and more distinctive. At magnitude 8.1, you will need a telescope to see the Dumbbell.

While searching for the Dumbbell Nebula, you may run across a small cluster of stars that draws your attention. This grouping is most popularly known as the Coathanger, but it also goes by the name of Brocchi’s Cluster or Collinder 399. These stars are not actually a physical cluster but just a smattering of stars that look like they are in close proximity due to the direction from which we are looking. In reality, the stars lie from between 218 and 1,132 light-years away. The stars of the Coathanger shine at magnitudes 5 and 6, within reach of keen eyes, but better with binoculars.

-- Kelly Kizer Whitt loves clean, clear, and dark skies. Kelly studied English and Astronomy at the University of Wisconsin-Madison and worked for Astronomy magazine. She writes the SkyGuide for AstronomyToday.com. You can follow her on Twitter at twitter.com/Astronomommy.


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