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The first known globular cluster, now called M 22, was discovered in 1665 by Abraham Ihle, a German amateur astronomer. [4] [5] [6] The cluster Omega Centauri, easily visible in the southern sky with the naked eye, was known to ancient astronomers like Ptolemy as a star, but was reclassified as a nebula by Edmond Halley in 1677, [7] then finally as a globular cluster in the early 19th century ...
The brightest star in the cluster is a red giant, the variable star V11, also known as V1554 Herculis, [16] with an apparent visual magnitude of 11.95. M13 is 22,200 to 25,000 light-years away from Earth , [ 9 ] and the globular cluster is one of over one hundred that orbit the center of the Milky Way.
It contains 274 known variable stars, by far the most found in any globular cluster. These include 133 RR Lyrae variables , of which about a third display the Blazhko effect of long-period modulation.
These new-found star clusters contain hundreds of thousands of stars, a similar number to globular clusters. The clusters also share other characteristics with globular clusters, e.g. the stellar populations and metallicity. What distinguishes them from the globular clusters is that they are much larger – several hundred light-years across ...
Messier 4 or M4 (also known as NGC 6121 or the Spider Globular Cluster) is a globular cluster in the constellation of Scorpius. It was discovered by Philippe Loys de Chéseaux in 1745 and catalogued by Charles Messier in 1764. [9] It was the first globular cluster in which individual stars were resolved. [9]
Located at a distance of 17,090 light-years (5,240 parsecs), it is the largest known globular cluster in the Milky Way at a diameter of roughly 150 light-years. [10] It is estimated to contain approximately 10 million stars, with a total mass of 4 million solar masses, [11] making it the most massive known globular cluster in the Milky Way.
Moving cluster parallax is a technique where the motions of individual stars in a nearby star cluster can be used to find the distance to the cluster. Only open clusters are near enough for this technique to be useful.
M22 is one of the nearer globular clusters to Earth – at about 10,600 light-years away. It spans 32 ′ on the sky which means its diameter (width across) is 99 ± 9 light-years, given its estimated distance. 32 variable stars have been recorded in M22.