Globular clusters are groups of stars that stick together because of their mutual gravity. This clusters are located in and around galaxy’s. They appear often and are a common appearance. In our galaxy alone, there are 150 known. Some globular clusters are very heavy and count’s millions of sun masses. They probably were once the cores of galaxies that evolved around an host galaxy, like the Magellanic Clouds evolve around the Milky Way. The most globular clusters contains hundreds of thousands of stars, but, with some exceptions, every globular cluster appears to have stars that are born at the same time.
Globular clusters are very stable because of their gravity. Stars can get so close to each other that they will collide. But there is also a lot of open space in a globular cluster.
Most globular clusters are very old and they probably took shape right after the beginning of the universe. They belong to the oldest objects known. There are a few globular clusters that are blue. This is an indication of young, hot stars. It’s not known yet if these clusters can form later on, but there are indications that they can also form when galaxies collide. Globular clusters form a big halo around galaxies. In and around every galaxy there are these clusters.
A lot of globular clusters are already visible through binoculars as a faint spot. On dark nights, the Hercules Globular Cluster (M13) is even visible naked eyed. Through small telescopes most clusters look like a fuzzy dot, but the bigger you’re telescope, the more detail you can observe.
Some globular clusters to observe for yourself
The Hercules Globular Cluster
This globular cluster (Messier 13) is discovered in 1714 by Edmond Halley in constellation Hercules. It’s age is rated at 14 billion years and it’s located at a distance of about 25.100 light years from earth. In 1764 Charles Messier catalogued the object in his catalogue as number 13 (M13).
With a magnitude of 5.8 you can see this object on dark, clear night with the unaided eye as a faint spot.
Messier 22 in constellation Sagittarius is discovered in 1665 by Abraham Ihle. Charles Messier gave it number 22 in his catalogue. With a distance of 10.400 light years away from earth, this is one of the most nearest globular clusters. It’s size measures 97 light years. The stars in this cluster (more than 100.000) evolve around the centre of the cluster. The cluster itself evolves around the centre of the Milky Way.
Messier 22 has a magnitude of 5.1 and it’s a good target for binoculars.
Nicolas Louis de Lacaille discovered this globular cluster in 1751 in constellation Sagittarius. Almost 30 years later, Charles Messier gave it number 55 in his catalogue. This cluster is located at a distance of 17.300 light years from earth and it has a size of 100 light years.
Messier 55 has a magnitude of 6.3 and it’s easy to see with binoculars on dark, moonless nights.