The Relative Ages of Galactic Globular Clusters

We discuss the present state of knowledge and thought concerning the spreadin age found among Galactic globular clusters, with some discussion of theimplications for what happened during the earliest stages of the formation ofthe Milky Way Galaxy. Differential observational techniques to derive therelative age differences among clusters of similar metallicity are discussed indetail. We conclude that as of the current date (mid-April 1996) the state ofthe field is still somewhat muddled. However, we believe that there is now asubstantial body of evidence --- including a particularly revealingintercomparison of the color-magnitude diagrams of \ngc{1851}, \ngc{288}, and\ngc{362} presented here --- indicating that age is {\it not\/} the dominantsecond parameter determining the shape of globular clusters' horizontalbranches. If our assertion is correct, then apart from a handful of anomalousclusters that may well have been captured from a satellite dwarf galaxy, thereis no strong evidence either for a significant spread in age among clusters ofa given metal abundance or for a systematic variation of mean age withGalactocentric distance. On the question of whether there is a significant agedifference between metal-poor and metal-rich clusters, we feel compelled tofall back on the Scottish verdict: ``Unproven.'' Data now being collected bynumerous groups in various subdisciplines may resolve the remaining controversywithin a few years.