Lines of constant R in the H-R diagram
Main sequence not quite
constant R
B stars:   R ~10 RSun
M stars:   R ~0.1 RSun
Betelgeuse:  R~ 1,000 RSun
Larger than 1 AU
White dwarfs:  R~ 0.01 RSun
A few Earth radii
What causes the “main sequence”?
Why “similar” size, with
precise R related to T?
Why range of T?
Why are a few stars (giants, white
dwarfs) not on main sequence?