Properties of Secondary Importance
A number of other observable factors may be determined for stars, but these generally are of minor importance in understanding stars as a whole. These include evidence for motions such as rotation or turbulence in stellar atmospheres, direct measurement of surface gravity, the presence of circumstellar material, and the strength of a magnetic field. Stars may also exhibit variability in luminosity and size (pulsating and other variables).
Stellar ages should be mentioned because age is a property of any star. But the reality is that age is not determinable directly for most stars and generally must be deduced from theoretical principles applied to understanding how stellar properties change over time. Thus stellar age is not an observational property.