How old is that star?
That is one of the most difficult questions to answer in galactic astrophysics. Of the fundamental properties that determine the state of a star (mass, composition and age, primarily), we can directly and accurately measure many stars' masses and then estimate the mass of a single star of the same spectral types. Similarly, stars directly reveal their compositions to us through their spectra. Many significant and interesting questions remain in studying the masses and compositions of stars, yet one can say that those subjects are well enough understood to know what the important questions are?
It is time to bring together astronomers from the around the world to discuss the current state of the problem of estimating ages of individual stars and of populations, where the advances are now being made, and what the near future offers.
The IAU Symposium #258 brought together astronomers and theorists from all over the world to Baltimore in 2008 to shed light on The Ages of Stars.