\magnification=\magstep1

$$
\theta \quad = \quad {{\rm 1\ AU}\over{d \rm \ pc}} 
       \quad = \quad
                   {{1.0 \rm \ arcsec}\over{d}}
$$

$$
\theta_{\rm Airy} \quad = \quad 1.22 \thinspace {{\lambda}\over{D}}
$$


$$
L \quad \gg \quad {{\pi D^2}\over{\lambda}}
$$

$$
L \quad \gg \quad D \qquad \qquad {\rm and\ } \quad L \quad \gg \quad \lambda 
$$

\bye