How to Identify the Keystone Asterism in Hercules
An asterism is a group of stars within a constellation or stars from different constellations that form a shape in the night sky. The Keystone asterism of Hercules is such a shape, but it is not easy to identify in the sky. First you have to find Hercules and then look for the Keystone. Here is a guide on how to identify the Keystone asterism in Hercules.
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Instructions
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How to Identify the Keystone Asterism in Hercules
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Go outside about 10 p.m. in northern latitudes on a moonless evening. The Keystone is not composed of bright stars, making it difficult to make out under good conditions. With moonlight it will be very hard to find and identify. Look for the Keystone during the early summer months.
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Face east and look for the brightest star in the sky. That would be Vega in Lyra the Harp, a brilliant star. The Keystone of Hercules lies to the right of Vega, between Vega and Arcturus, another bright star in Bootes.
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The Keystone is an uneven rectangular shape, with one end longer than the other. It is made up of four stars, none brighter than second magnitude. As you look at Hercules you will see the Keystone, with the longer end of the quadrangle on the top.
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If you have a small telescope or a pair of good binoculars you can look for the Great Globular Cluster. It is located in the Keystone and is comprised of hundreds of thousands of stars. It is visible to the naked eye but is best found with help. The Great Globular Cluster is on the right side of the Keystone, located on the upper part of a line from the top right Keystone star to the bottom right.
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To be sure you have found the Keystone asterism in Hercules look for a crown. Corona Borealis, the Northern Crown, is to the lower right of the Keystone. It is a "U" shaped constellation that is opened towards the Keystone. Another globular cluster almost as bright as the Great Globular Cluster is to the upper left of the Keystone, but not within its boundaries.
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- Photo Credit rellimcire.blogspot.com
