As summer officially begins this month, it is a great time to use binoculars to search for the celestial gems of summer. These star clusters are made up of large group of stars that are shaped into round objects like a globe, hence the name globular clusters.
Globular clusters are found around the halo of the Milky Way galaxy. It was discovered that these objects were all about equal distance from the Milky Way. This led to the size of the Milky Way being found.The number of stars that are in these objects range from 10,000 to more than a million. There are about 180 globular clusters in the Milky Way.
One of the oldest known globular clusters is Omega Centauri. It was visually recorded by Ptolemy in 150 AD as a star. Omega Centauri is large as the full moon, but it is about 16,000 light years away. It wasn’t until 1677 that the object was reclassified by Edmond Halley.
It wasn’t until 1826 that it was classified as a globular cluster. It is visible from the Ozarks, but very close to the southern horizon. I have viewed it on three different occasions. Its stars fill the eyepiece of the telescope.
Messier 13 (M13) is one of the better known globular clusters. It is also known as the Great Globular Cluster in Hercules. Located in the keystone of Hercules, M13 can be viewed with the unaided eye at a very dark site. Easily seen in binoculars, this object is a site to view through any telescope. With even larger telescopes, a spiral pattern and the color of the different stars can be seen. M13 contains hundreds of thousands of stars. It is around 25,000 light years away.
Globular clusters generally contain stars that have reached the end of their life cycle. Stars in globular clusters are densely packed. Whereas the nearest star to Earth is more than four light years away, stars inside a globular cluster are a light year apart from each other. They may be as close together as Pluto is to the sun.
Globular clusters have been found in other galaxies. The Andromeda galaxy has over 460 clusters located in it. The galaxy Messier 87 has at least 13,000 of these objects.
During the summer, more than 100 of them can be found during the night.
Summer solstice, the longest day of the year, officially arrives on June 20.
Mercury will be at its brightest on June 4. Look towards the western sky about 30 minutes after sunset.
Jupiter and Saturn will close together during the middle of the month. The Moon will be close to both planets on the morning of June 8.
Mars and the Moon will be close on the night of June 12.
The Springfield Astronomical Society meets every fourth Tuesday of the month the Library Center at 4653 S. Campbell Ave., Springfield. Please check our web site (http://www.springfieldastronomy.org) for our next scheduled meeting.