Observing M5

During these summer vacation months, if you find yourself under dark skies and you are equipped with quite powerful binoculars (at least a 10x50) do not miss to observe the globular cluster M5! In the direction of the constellation Serpens near the star Unukalhai you can in fact see this object of magnitude 6.7, which through binoculars appears as a nebulous spot, while through telescopes it reveals all its beauty.

M5 is located 25,000 light-years away from Earth and contains more than 100,000 stars enclosed in a sphere with a diameter of 165 light-years. With an estimated age of 13 billion years, M5 is one of the oldest known globular clusters.

As can be understood from the different colors of the image, the stellar population of the cluster is very varied. Inside it there are in fact several red and blue giants, while most of the stars are yellow. M5 also contains many variable stars: 105 have been discovered, most of which are RR Lyrae. These are advanced evolutionary stars that have finished the central hydrogen burn and started the helium burn. Their brightness variation is due to periodic radial pulsations.

Credit: Adam Block, Mt. Lemmon SkyCenter, University of Arizona.