THE AGE OF THE GALACTIC GLOBULAR-CLUSTER SYSTEM

A careful assessment of current uncertainties in stellar physics (opac ities, nuclear reaction rates, equation of state effects, diffusion, r otation, and mass loss), in the chemistry of globular cluster (GC) sta rs, and in the cluster distance scale, suggests that the most metal-po or (presumably the oldest) of the Galaxy's GCs have ages near 15 Gyr. Ages below 12 Gyr or above 20 Gyr appear to be highly unlikely. If the se approximate to 2 sigma limits are increased by similar to 1 Gyr to account for the formation time of the globulars, and if standard Fried mann cosmologies with the cosmological constant set to zero are assume d, then the GC constraint on the present age of the Universe (t(0) gre ater than or equal to 13 Gyr) implies that the Hubble constant H-0 les s than or equal to 51 km s(-1) Mpc(-1) if the density parameter Omega = 1 or less than or equal to 62 km s(-1) Mpc(-1) if Omega = 0.3.