Uncertainites in Ages
The ages of globular clusters are inferred
from the population of stars they contain, using theoretical models of the time it
would take to form the observed population. Uncertainties in the stellar models,
coupled with uncertainties in the luminosities of distant stars and in the age of the
Universe,
presumably explain why some globulars are estimated to be
slightly older than the Universe itself (which is obviously not possible). As we noted
earlier in Chapter 18, revised distance scales to stars based on Hipparcos parallax
measurements may have removed some of these discrepancies.