Milwaukee Astronomical Society



The Constellation Hercules

  1. Now as you go to the west, or to the right, of Lyra, you come upon another important asterism, "The Keystone". Just like it says, it is four stars in the shape of a keystone. {Trace out the Keystone.} And like the other asterisms it is a part of a larger constellation - the constellation Hercules. {Trace out Hercules.} The star that represents Hercules' head, α Herculis, is another red supergiant like Antares - by most estimates it's a little closer than Antares and since it's not as bright, we presume it is smaller. With a good telescope you can see that this reddish-orange star has a blue-green companion.

  2. One of the reasons for finding the Keystone is to help locate M13 - the brightest and best globular cluster in the Northern Hemisphere. Globular clusters are rare - only about 150 are known, and they are completely different from open clusters like the Butterfly Cluster that we saw in Scorpius.

    The Butterfly is estimated to be about 100 million years old, M13 is estimated at about 10 BILLION years old, making it so old that it formed before the disk of the Milky Way galaxy formed! While the Butterfly cluster has maybe 100 stars in it total, M13 has no less than 1 million stars. The Butterfly cluster is about 1200 light-years away and about 20 light-years across, M13 is 20,000 light-years away and 160 light-years across.

    These numbers are typical, so globular clusters are much, much bigger than open clusters, and they are much, much older - some are nearly as old as the universe!

    M13 - Hercules Cluster

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Your questions and comments regarding the Stargazing section are welcome. You can e-mail the author, Randy Culp for inquiries, suggestions, new ideas or just to chat.
Updated 18 July 2023