A globular star cluster is a large grouping of stars that are gravitationally drawn together into a more concentrated spherical shape than open star clusters. About 150 Milky Way globular star clusters have been identified to date. A cluster can contain upwards of a million stars. It forms a regular sphere with the density of stars increasing towards the center. Some clusters are predominately comprised of bluish stars which indicate that they are younger than those which have a larger proportion of reddish stars.
The poster shows 25 of my favorite globular clusters out of the 75 that I have imaged. The clusters are shown on the poster ordered by name.
Globular clusters are an acquired taste in this hobby - some people love them, most could probably do without them. At a distance (and sometimes even close), they may appear to look similar. Until I started imaging many of them, I did not appreciate their differences or similarities. The color, brightness and pattern differences are often subtle, but once realized they become fascinating targets and no two truly are alike.
Highlights of the poster include:
- NGC 5139 (Omega Centauri) - My favorite globular cluster, this magnificent object is located 16,000 light years away in the southern sky constellation of Centaurus. One of the few globular clusters visible to the naked eye, it is the largest globular cluster in the Milky Way at a diameter of 150 light-years and is estimated to contain 10 million stars. It is one of the earliest documented deep sky objects, described in 150 A.D. by Ptolemy.
- M13 - This object is one of the sky's best globular clusters and my favorite one in the northern hemisphere. It is located 25,000 light years away in the constellation of Hercules. This cluster is about 145 light-years in diameter.
- M55, NGC 288, and NGC 6723 - Three of my favorite of the lesser known, underappreciated globular clusters.
- NGC 2419 - This object is a globular cluster located an astounding 300,000 light years away in the constellation of Lynx. It has the nickname - "The Intergalactic Wanderer". It is believed that this is an extragalactic cluster, belonging to the Sagittarius Stream of the Sagittarius Dwarf Spheroidal Galaxy (SDSG). Its orbit around the Milky Way is a long one, taking 3 billion years to make one trip around our galaxy
- G1 (Mayall II) - This is another extragalactic cluster. It is the smallest cluster on the poster in our apparent view, but the largest in actual size. It is located 2.5 million light years away in the Andromeda Galaxy and has a diameter of 300 light years. G1 is the brightest of 500+ globular clusters that have been identified so far as belonging to the Andromeda. G1 is believed to have twice the mass of Omega Centauri.
Each of the clusters of the poster has previously been uploaded and described individually on Astrobin. They all reside in my
Astrobin Globular Cluster Collection.
The technical data for the clusters on the poster is shown on Revision B.
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