A telescope mirror with diameter $D = 200$ inches observes a star emitting $\lambda = 5000$ Å. Its angular limit of resolution is approximately:
A$1.2 \times 10^{-7}$ rad
B$1.2 \times 10^{-5}$ rad
C$1.2 \times 10^{-3}$ rad
D$0.5$ arcsec
Answer & Solution
Correct answer: A. $1.2 \times 10^{-7}$ rad
200 inches = 5.08 m. $\theta = 1.22\lambda/D = 1.22 \times 5 \times 10^{-7}/5.08 \approx 1.20 \times 10^{-7}$ rad. (Hale telescope-scale.)
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