The constellation Hercules is high in the east as darkness falls. It takes a bit of imagination to see a mythical human figure in the pattern of stars that make up the constellation, but the central “keystone” shape is easy to see. In between the two western stars of this keystone sits a jewel of the night sky, the globular cluster M13.
Globular clusters are dense collections of stars that orbit the galactic cores of most galaxies. We have discovered about 150 globular clusters in our own Milky Way galaxy. Globular clusters are beautiful objects through a telescope, with high magnification and resolving power revealing hundreds to thousands of individual stars.
M13, also called the Great Hercules Cluster, was discovered in 1714 by Edmund Halley, who also discovered the well-known comet that bears his name. In 1764, Charles Messier added it to his list of bright deep sky objects.
Messier was also a comet hunter, but he is most famous for making a list of objects that were not comets. This list of 110 objects is now known as the "Messier Catalog." Observing Messier objects is a rite of passage for amateur astronomers. We’ve discussed a few of these objects in past columns, including M42, M45, and M44.
The Hercules cluster contains hundreds of thousands of stars. It is about 150 light years in diameter and approximately 25,000 light years away. We believe that most globular clusters formed relatively early in the history of the universe, with M13 forming about 11.5 billion years ago.
Most of the stars in the cluster are of a similar age and are what’s known as population 2 stars. This is the generation of stars that preceded stars like our sun.
M13 is easy to find. Try using an astronomy app and a pair of binoculars.
You’ll see a round fuzzy patch that is clearly not a star. If you’re lucky enough to have access to a telescope you’re in for a treat.
If you don’t have access to optical aid, you can still find the constellation of Hercules. As you observe, try to imagine what your night sky would look like if you lived in the center of a globular cluster, where there are so many bright stars nearby that starlight might eliminate the darkness of night.
The Morning Sky
Three bright planets wait for you in the morning sky. Jupiter and Saturn rise before midnight and are high in the south before dawn. Mars rises around 2 a.m. and is an easy target. The red planet is visible in the south east in the early morning. The moon pairs closely with Mars on the 12th and 13th.
The Evening Sky
Mercury is diving toward the sun, but you can still spot it if you have a clear view to the western horizon. Look low in the west-north-west right around twilight. In the eastern sky after sunset is the constellation Hercules. To the east of Hercules is the bright star Vega, one of the points of the Summer Triangle.
Dan Price is a NASA/JPL Solar System Ambassador and informal educator. He leads the Night Sky Tours at Josephine Sculpture Park. He just helped yet another budding young astronomer find his first telescope.
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