Answer
$1.7\times10^{11}m$
Work Step by Step
Find the angular resolution using equation 25–7.
$$\theta=\frac{1.22\lambda}{D}$$
The distance between the stars, L, is that angle multiplied by the distance to the stars from the Earth, r.
$$L=r \theta=1.22\frac{r \lambda}{D}$$
$$L= 1.22 \frac{(18ly)(9.46\times10^{15}m/ly)(550\times10^{-9}m)}{0.66m}$$
$$L= 1.7\times10^{11}m$$
