Messier 5 (M5) is a globular star cluster located in the constellation Serpens. M5 is among the largest and most ancient globular clusters visible in the night sky. It contains around 500,000 stars and boasts one of the highest concentrations of variable stars. M5 is about 24,500 light-years from Earth and is estimated to be 13 billion years old, making it one of the oldest known clusters.