In late spring, from mid-northern latitudes, you can easily find the brilliant star Vega in the eastern sky at dusk and nightfall. The brilliant blue-white star Vega acts as your guide star to the Keystone, a wedge-shaped pattern of four stars in the constellation Hercules.
Look for the Keystone asterism – star pattern – to the upper right of Vega. Or hold your fist at arm’s length, it’ll easily fit between Vega and the Keystone.
Also, you can locate the Keystone by using Vega in conjunction with the brilliant yellow-orange star Arcturus. The Keystone is found about 1/3 of the way from Vega to Arcturus, the two brightest stars to grace the Northern Hemisphere’s spring and summertime sky. From mid-northern latitudes this time of year, Arcturus is found quite high in the eastern sky at nightfall and evening. Then, by late evening, Arcturus will have moved high overhead.
Use the Keystone to find M13
Furthermore, the Keystone is your ticket to find a famous globular star cluster in Hercules, otherwise known as the Hercules cluster, aka Messier 13 or M13.
Most likely, you’ll need binoculars to see the Hercules cluster. Although sharp-eyed people can see it with the unaided eye in a dark, transparent sky. But through binoculars, this cluster looks like a dim smudge or a somewhat fuzzy star. However, a telescope begins to resolve this faint fuzzy object into what it really is, a great big, globe-shaped stellar city populated with hundreds of thousands of stars!
Then, later in the evening, the Keystone and the Hercules cluster swing high overhead after midnight, and are found in the western sky before dawn.
Photos of M13 from EarthSky Community Photos
Bottom line: Let the bright star Vega guide you to a famous star pattern in Hercules – called the Keystone – and then to the Hercules cluster, aka M13, a famous globular star cluster.
Bruce McClure served as lead writer for EarthSky's popular Tonight pages from 2004 to 2021, when he opted for a much-deserved retirement. He's a sundial aficionado, whose love for the heavens has taken him to Lake Titicaca in Bolivia and sailing in the North Atlantic, where he earned his celestial navigation certificate through the School of Ocean Sailing and Navigation. He also wrote and hosted public astronomy programs and planetarium programs in and around his home in upstate New York.
Like what you read? Subscribe and receive daily news delivered to your inbox.
Thank you! Your submission has been received!
Oops! Something went wrong while submitting the form.