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Find the Keystone in Hercules, and the Hercules Cluster M13


Star chart of man-shaped constellation with bent arms and legs, and several labeled stars.
Hercules is a faint constellation. But its mid-section contains the easy-to-see Keystone asterism, that is, a star pattern. You can find Hercules between the bright stars Vega in Lyra the Harp, and Arcturus in Boötes the Herdsman. And once you find the Keystone, you can easily locate M13, the Hercules cluster. Chart via EarthSky.

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Use Vega to locate the Keystone in Hercules

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, in Lyra the Harp, 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, in Boötes the Herdsman. 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. Then, by late evening, Arcturus moves high overhead.

Star chart of man-shaped constellation with bent arms and legs, squarish in the middle with a labeled cluster.
Before you can find M13, you need to find the Keystone in Hercules, a pattern of 4 stars. So as darkness falls, look for the Keystone to the upper right of the brilliant star Vega. Chart via EarthSky.

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.

White star chart with black dots and lines showing keystone shape and lines radiating outward.
Can you find the Keystone on this chart? See the compact grouping of 4 stars at the center of Hercules? That’s it. Note the whereabouts of Messier 13 within the Keystone pattern. Also, above the Keystone is another globular cluster, M92. It’s a bit smaller and dimmer than M13, but also easy to pick up in binoculars or a telescope. Image via International Astronomical Union/ Sky & Telescope/ Wikimedia Commons (CC BY 3.0).

Photos of M13 from EarthSky Community Photos

A large, spherical cluster containing thousands of bright bluish stars, inside a yellow circle with labels.
View at EarthSky Community Photos. | Tameem Altameemi in the United Arab Emirates (UAE), captured this telescopic view of the great Hercules Cluster on April 26, 2025. Tameem wrote: “This image features the beautiful globular cluster Messier 13, also historically known as the Al-Jathi Cluster. Located in the constellation Hercules, M13 lies about 22,200 light-years away from Earth and has an estimated age of 11.65 billion years. It contains several hundred thousand ancient stars, densely packed into a region about 213 light-years across. In the same field of view, the spiral galaxy NGC 6207 and the faint active galaxy IC 4617 are visible.” Thank you, Tameem!
A large, spherical cluster containing myriads of bright white stars, denser toward the middle.
View at EarthSky Community Photos. | Tom Cofer in Lakewood Ranch, Florida, captured this telescopic view of Messier 13, the Great Globular Cluster in Hercules, on March 14, 2025. Tom wrote: “A snow globe of stars!” Thank you, Tom!
A large, spherical cluster, denser in the middle, containing thousands of bright yellowish stars.
View at EarthSky Community Photos. | Stephen Montag in Livingston, New Jersey, captured this telescopic view of Messier 13 on May 24, 2024. Stephen wrote: “The Great Hercules Cluster, consisting of several hundred thousand stars. Located 25,000 light-years from Earth.” Thank you, Stephen!

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.

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The post Find the Keystone in Hercules, and the Hercules Cluster M13 first appeared on EarthSky.



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Star chart of man-shaped constellation with bent arms and legs, and several labeled stars.
Hercules is a faint constellation. But its mid-section contains the easy-to-see Keystone asterism, that is, a star pattern. You can find Hercules between the bright stars Vega in Lyra the Harp, and Arcturus in Boötes the Herdsman. And once you find the Keystone, you can easily locate M13, the Hercules cluster. Chart via EarthSky.

Looking up has never felt more important. Please donate to help EarthSky keep bringing the sky to your screen.

Use Vega to locate the Keystone in Hercules

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, in Lyra the Harp, 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, in Boötes the Herdsman. 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. Then, by late evening, Arcturus moves high overhead.

Star chart of man-shaped constellation with bent arms and legs, squarish in the middle with a labeled cluster.
Before you can find M13, you need to find the Keystone in Hercules, a pattern of 4 stars. So as darkness falls, look for the Keystone to the upper right of the brilliant star Vega. Chart via EarthSky.

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.

White star chart with black dots and lines showing keystone shape and lines radiating outward.
Can you find the Keystone on this chart? See the compact grouping of 4 stars at the center of Hercules? That’s it. Note the whereabouts of Messier 13 within the Keystone pattern. Also, above the Keystone is another globular cluster, M92. It’s a bit smaller and dimmer than M13, but also easy to pick up in binoculars or a telescope. Image via International Astronomical Union/ Sky & Telescope/ Wikimedia Commons (CC BY 3.0).

Photos of M13 from EarthSky Community Photos

A large, spherical cluster containing thousands of bright bluish stars, inside a yellow circle with labels.
View at EarthSky Community Photos. | Tameem Altameemi in the United Arab Emirates (UAE), captured this telescopic view of the great Hercules Cluster on April 26, 2025. Tameem wrote: “This image features the beautiful globular cluster Messier 13, also historically known as the Al-Jathi Cluster. Located in the constellation Hercules, M13 lies about 22,200 light-years away from Earth and has an estimated age of 11.65 billion years. It contains several hundred thousand ancient stars, densely packed into a region about 213 light-years across. In the same field of view, the spiral galaxy NGC 6207 and the faint active galaxy IC 4617 are visible.” Thank you, Tameem!
A large, spherical cluster containing myriads of bright white stars, denser toward the middle.
View at EarthSky Community Photos. | Tom Cofer in Lakewood Ranch, Florida, captured this telescopic view of Messier 13, the Great Globular Cluster in Hercules, on March 14, 2025. Tom wrote: “A snow globe of stars!” Thank you, Tom!
A large, spherical cluster, denser in the middle, containing thousands of bright yellowish stars.
View at EarthSky Community Photos. | Stephen Montag in Livingston, New Jersey, captured this telescopic view of Messier 13 on May 24, 2024. Stephen wrote: “The Great Hercules Cluster, consisting of several hundred thousand stars. Located 25,000 light-years from Earth.” Thank you, Stephen!

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.

Enjoying EarthSky so far? Sign up for our free daily newsletter today!

EarthSky astronomy kits are perfect for beginners. Order today from the EarthSky store

The post Find the Keystone in Hercules, and the Hercules Cluster M13 first appeared on EarthSky.



from EarthSky https://ift.tt/t7uxq3I

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