How accurately are the ages of the Encyclopedia stars known?
Stellar ages are the most uncertain data in the Encyclopedia. The main method for estimating ages, based on Ca H and K emission line strengths, can have an uncertainty of 100% (contrast this with the ~1% for distance and ~25% for composition described above). This is still normally sufficient to discriminate between very young, medium, and old stars. Nevertheless, data for ages are not very precise. I quote stellar ages to two significant digits, but in practice this is too much precision. There are other ways of estimating stellar ages. The most reliable — probably more reliable for many stars than the Ca emission measurements — involves stellar evolution theory and models. Astronomers have calculated how the luminosity and spectrum of a star vary as a function of various parameters, notably stellar mass, composition, and age. In principle, if the luminosity, spectrum, mass, and composition of a star are well characterized, the age can be determined from these models of stellar evol
