This month look for the Keystone of Hercules. The Keystone consists of four stars arranged in a keystone, or truncated triangle shape. The Keystone represents the body of the hero Hercules. His arms and legs are arranged such that he is upside down and kneeling.

Find the Keystone by first locating Vega, the brilliant blue-white star located nearly overhead just after dark. From Vega, look 16 degrees to the west-southwest for keystone pattern of four stars. Sixteen degrees is about the width of your hand and extended thumb when viewed from your outstretched arm.

The stars of the Keystone, clockwise from the upper left are Pi, Eta, Zeta, and Epsilon Herculis. Although the Keystone appears flat against the sky, it’s actually three-dimensional. Pi is 370 light years, Eta 112 light years, Zeta 35 light years, and Epsilon 163 light years away. However, these distances pale in comparison to the distance to the fuzzy cloud located between Eta and Zeta (the side of the keystone away form Vega). That fuzzy cloud is M-13, the Hercules Globular Cluster and its located 25,000 light years away. In a pair of binoculars, M-13 looks like a fuzzy star. You’ll know you’re looking at it when all the stars appear as sharp pin points of light, except for this one. M-13 is more impressive through a telescope though. A good telescope will resolve the cluster into a ball of tiny stars immersed in fog. In a large telescope, M-13 looks like a pile of salt on blackest velvet.

July Overview

• The length of the day shortens by 46 minutes this month
• Mercury and Venus make a close, but low approach on the morning of the 17th
• Earthshine on the moon is visible in the evening on the 1st and again in the morning starting on the 22nd
• The moon approaches Venus the morning of 24th
• The moon approaches Mars the evening of the 5th.
• The moon approaches Saturn the evening of the 7th.