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Deepsky Top-100 (12): M 13, the Great Globular Cluster in Hercules

Edmond Halley discovered M 13 in 1714. It is one of the finest globular clusters of the northern celestial hemisphere you can observe from your own backyard. M13 has a visual diameter of 14' and a visual magnitude of 5.7. The cluster lies at a distance of 25,000 light years and contains several 100,000 stars.

M 13 is very easy to locate. Between the constellations of Lyra and Corona Borealis lies the central part of the constellation Hercules, a sort of square formed by four stars. This asterism of four stars is also known as "The Keystone". As you can see on the map, M 13 lies about 2 degrees south of Eta Herculis, 1/3 of the distance from Eta to Zeta.

Finder chart for M 13. Limiting magnitude 6.5
Credit and copyright SkyTools 2 by Capellasoft

Click here to download a printable finder chart (PDF)

From a dark sky site, M 13 is a naked eye object, but from a light polluted backyard, you will have to use some optical aid to find it. M13 can be spotted with binoculars. In my 7x50 and 15x80 it looks like a fuzzy ball of light. In the 8-inch telescope, using a magnification 0f 166x I can detect many individual stars across the core of the cluster. When the seeing is good, I can also detect several arms with stars coming out of the core of M 13. It looks like a sort of "propeller".

I once had the chance to see M 13 from a dark sky site with a high quality 12-inch Dobson telescope. It looked more beautiful than on all the images I had ever seen in all the books and magazines. The core was completely resolved into thousands of bright stars. The "propeller" arms coming out of the core looked stunning. Actually the whole cluster looked 3-D. Anyway, M 13 is one of the best globulars to observe, so whatever telescope you own, give it a try. Use different magnifications to see what works best for you.

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