Exploring the constellation of Hercules

Hercules is a constellation that is visible high in the summer sky, but also lower in the western horizon of the winter sky. For me, it is a constellation that i enjoy observing in the months of October and November as it is in the best position for my location. Hercules is not the brightest of constellations. Hercules’ Alpha star, Rasalgethi has a magnitude of only 3.1, however Hercules is still easy to spot in the sky due to its characteristic centre which is made up of 4 stars and is known as the keystone. Hercules is the 5th largest constellation in the entire night sky and is well known for its fantastic globular star clusters.

The great globular cluster in Hercules (M13) (photo credit:

At a magnitude of 5.7, the great globular star cluster or M13, should be visible to the naked eye, however in most areas it will be hard to see without binoculars or a small telescope, and it is only in unpolluted skies that it is visible to the naked eye, but only as a small hazy star. therefore, it is much easier to appreciate its wonder by observing it through a small telescope. Globular star clusters are made up of thousands of older stars, quite the opposite to the young open star clusters such as the Pleiades in Taurus, and M13 contains around 250,000 stars, most of which are around 12 million years old. M13 is not easy to find in the sky the first time round. I have been lucky to see it twice and the first time I found it, it took over half an hour to find it. M13 sits in between the two stars of Eta Herculis and Zeta Herculis. M13 is around one-third the distance between theses two stars, closer to Eta Herculis. once you find it, it will first appear slightly hazy depending on the size of your telescope (I used a 5 inch reflector to observe it) but as your eyes adjust you will be able to pick out individual stars. M13 was one of my first truly deep sky objects that I observed and it was very rewarding to see it.

Hercules is also home to another globular star cluster under the name of M92, which is not as bright as M13, but still an impressive sight when viewed through a small telescope. It has a magnitude of 6.5 meaning it is not possible to see it at all with the naked eye, but will become clear in binoculars and is well worth seeing.



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