By Deborah Byrd
Friday, April 25
The constellation Hercules the Kneeling Giant can be seen ascending in the east-northeast on these spring evenings. Our chart today shows the sky for late night, when all of these objects are well up in the northeastern to eastern sky.
The stars Arcturus and Vega can help you identify Hercules, whose most noticeable pattern is a squarish figure in the center of the constellation. This sky pattern, or “asterism,” is known as the Keystone in Hercules.
The Keystone is a helpful pattern for more reasons than one. First, it’s noticeable on the sky’s dome and can lead your eye to Hercules. Also, the Keystone in Hercules can help you find the most fascinating telescopic object within the boundaries of this constellation. This object is a globular star cluster. Known to stargazers as M13 or the Great Cluster in Hercules, it’s barely visible to the eye alone in the darkest of skies.
Binoculars show M13 as a nebulous patch. And telescopes show stars both on the periphery of the cluster and toward its center. For a picture of M13 from the NOAO Image Gallery, look here: http://www.noao.edu/image_gallery/html/im0551.html.
This beautiful object is one of the galaxy’s oldest inhabitants. It’s a tightly packed spherical collection of about one million stars.