The Keystone
HemisphereNorthern Sky
AreaPart of Hercules
SymbolAsterism
About The Keystone
Four stars of Hercules form a lopsided quadrilateral shaped like the wedge stone of an arch. It is the easiest way to recognize this large but dim constellation. The Great Globular Cluster M13 lies on its western edge, visible to the naked eye as a fuzzy star under dark skies, with the fainter cluster M92 nearby. A useful stepping stone toward the Virgo cluster of galaxies.
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