What fundamental property of a star
varies along the main sequence?
T and R vary smoothly (and together) along the main sequence
B stars are ~4 times hotter and ~10 times bigger than sun
M stars are ~2 times cooler and ~10 times smaller than sun
Presence of a line implies that a single fundamental property
is varying to make some stars B stars and some stars M stars
That fundamental property then controls T, R
A second property controls whether we get a giant or dwarfs
Fundamental properties we could measure
Location:�� ����� Doesn�t seem to be of major importance
Composition:Outside composition of most stars similar (H, He, ...)
Age:�� ����� Will be important � but put off till Chapter 9
Mass:�� ����� Turns out to be the most important parameter