Abstract

Stellar spectral libraries are a crucial tool for interpreting the integrated spectra of distant galaxies. However, the process is far from trivial. Some limitations to our understanding of stellar evolution and galaxies are discussed, based on historical and recent results for the much more accessible, and apparently simpler, star clusters in our Galaxy. These include practical limitations imposed by the available data and what we can observe, and by our still incomplete theories of star formation and stellar evolution. At a deeper level, we may be biassed by the way that stellar evolution theory has itself evolved to explain specific types of objects. For example, in the case of globular clusters, we lack observational templates for the evolution of young (massive) metal-poor stars, and it is likely that different evolutionary processes occur for stars in such dense environments. The on-going explosion in the quantity and quality of available data keeps giving us fresh insights, and raising new questions.