April 19, 2014
Messier 92, a globular cluster in Hercules
Image Credits: NASA, ESA, the Hubble Heritage Team and WikiSky’s snapshot tool
Messier 92 (also known as NGC 6341) is a globular star cluster of some 109 light-years across. It is located about 26,700 light-years away from Earth in the northern constellation of Hercules, around 16,000 light-years above the Galactic Plane and 33,000 light-years from the Galactic Center. This cluster is approaching us at 112 kilometers per second.
Its age is estimated at 14.2 ± 1.2 billion years(!!), or roughly the age of the Universe. Messier 92 is one of the oldest globulars known and one of the brightest globular clusters in the northern hemisphere. Messier 92 has a mass of roughly 330,000 times the mass of our Sun.
Characteristic of globular clusters, Messier 92 has a very low abundance of elements other than hydrogen and helium (its “metallicity”). Relative to the Sun, the abundance of iron in the cluster is only 0.5% of the solar abundance, hence it is estimated to have roughly the age of the Universe.
Messier 92 is visible to the naked eye under very good conditions, but it is often overlooked by amateur astronomers because of its proximity to the even more spectacular Messier 13.