\magnification=\magstep2

$$
L = (4 \pi R^2) \sigma T_{eff}^4 
$$

$$
f (v, v+\Delta v) = {  {( {{m}\over{2 \pi k T}} )}
                        e^{-mv^2 / 2kT} 4 \pi v^2 \Delta v }
$$


$$
t_{age} \equiv { {P}\over{dP/dt} }
$$

$$
H \equiv { {T}\over{dT/dr} }
$$


\bye
