M5 is one of the finest and oldest globular clusters in the northern sky, lying around 24,500 light-years away in the constellation Serpens. Estimated to be around 13 billion years old — nearly as old as the universe itself — it contains several hundred thousand stars packed into a sphere roughly 165 light-years across. At its core, stellar densities are so extreme that stars are separated by only fractions of a light-year. M5 is notable for its unusually large population of RR Lyrae variable stars, making it a key calibrator for the cosmic distance ladder.