\magnification=\magstep1 

$$
\eqalign{
{ {\rm Brightness\ of\ planet} \over {\rm Brightness\ of\ star} } \quad =
  \quad {{ B_p } \over {B_s}} \quad &= 
  \quad {  {\rm surface\ area\ of\ planet } \over {\rm surface\ area\ of\ star} }  \cr
  \phantom { 3 } \cr
  &= \qquad { {4 \pi R_p^2} \over {4 \pi R_s^2} } \cr
  \phantom { 3 } \cr
  &= \qquad {\left(  {R_p} \over {R_s} \right)}^2  \cr
}
$$

$$
\eqalign{
{ {\rm Brightness\ of\ planet} \over {\rm Brightness\ of\ star} } \quad =
  \quad {{ B_p } \over {B_s}} \quad &= 
  \quad {  {\rm surface\ area\ of\ planet } \over {\rm surface\ area\ of\ orbit} }  \cr
  \phantom { 3 } \cr
  &= \qquad { {4 \pi R_p^2} \over {4 \pi r_{orb}^2} } \cr
  \phantom { 3 } \cr
  &= \qquad {\left(  {R_p} \over {r_{orb}} \right)}^2  \cr
}
$$


\bye
