4
How are L,
T, and R related?
•L
= area ´sT4 = 4 p R2 sT4
–Stars
can be intrinsically bright because of either large R or large T
–Use
ratio equations to simplify above equation
•(Note
book’s symbol for Sun is circle with dot inside)
–Example: Assume T is different but size is
same
•A
star is ~ 2 ´ as
hot as sun, expect L is 24 = 16 times as bright
•M
star is ~1/2 as hot as sun, expect L is 2-4 = 1/16 as bright
•B
star is ~ 4 ´ as hot as sun, expect L is 44 = 256 times as
bright
–Example: Assume T same but size is
different
•If
you have a G star 4 ´ as large as sun, expect L would be 42=16 times as bright
