Globular cluster M5. Optical image of the globular star cluster M5 (NGC 5904). North is at top. This cluster of stars lies some 25,000 light years from Earth in the constellation Serpens Caput. Globular clusters are huge balls of old stars which exist in a halo around our galaxy. M5 contains some 100,000 stars in an sphere with a diameter of over 130 light years. It is around 13 billion years old, one of the oldest globular clusters known. The bright star below and to the left of M5 is 5 Serpentis.