M5 (NGC 5904)
Distance: 24,500 light years

Right Ascension: 15 : 18.6 (hours : minutes)
Declination: +02 : 05 (degrees : minutes)

M5 is one of the oldest globular clusters with an estimated age of 13 billion years. Its photographic diameter is about 165 light years with a tidal diameter (beyond which member stars would be torn away) of over 200 light years. The cluster shows an intermediate level of metallicity. Metallicity is a term used that refers to elements heavier than helium, although some heavier elements like carbon for instance, are not really metals. These heavier elements were not present when the universe formed and could only be created through nucleosynthesis within the cores of stars. Although globulars as a group are metal deficient they are divided into metal poor and metal rich groups. The metal rich groups still have much lower metallicity than a younger star like our sun. This is called the Oosteroff dichotomy. Metallicity is estimated by analyzing the spectra of a star and computing the Iron to hydrogen ratio (Fe/H). An FE/H <2.0 places a globular in the metal poor group. Metallicity seems to decrease with distance from the galactic center suggesting a possible separate origin or even a captured origin of metal poor globulars from a dwarf satellite galaxy in the remote past.