[math-fun] oldest stars?

New York Times science section today discusses very old stars, in our galaxy, found by searches for ones with very small iron content. They then claim the oldest confirmed age of a star is 13.2 Gyr, confirmed by use of uranium and thorium half-lives. http://phys.org/news98033554.html QUESTION: Huh? How can you date a star by measuring its U and Th isotope content? It seems to me you'd have to know its isotope ratios when it started, and you don't. Obviously, these stars are not the oldest, since they contain iron that came from still-older stars -- but they come close to being first generation. -- Warren D. Smith http://RangeVoting.org <-- add your endorsement (by clicking "endorse" as 1st step)