Globular Cluster NGC 6397 (also known as NGC 6397) is a globular cluster in the Ara constellation. It is located about 7,200 light years from Earth, making it one of the two nearest globular cluster to Earth (the other one being Messier Object 4).
Estimating the age of the Milky Way
In 2004, a team of astronomers (as cited in "References") focused on the Cluster to estimate the age of the Milky Way. (The team consisted of Luca Pasquini, Piercarlo Bonifacio, Sofia Randich, Daniele Galli, and Raffaele G. Gratton.) The team used the UV-Visual Echelle Spectrograph of the Very Large Telescope to measure, for the first time, the Beryllium content in two stars in the Cluster. This allowed them to deduce the time elapsed between the rise of first generation of stars in the entire Galaxy and the first generation of stars in the Cluster. They added that estimate to an estimated age of the stars in the Cluster to arrive at an age of the Galaxy.
References