Answer to Question #142 in Optics for Shaleah

Question

One of the crucial possible methods of increase of resolution ability radio system application for observation of radiation of space mass means to use diffraction maximum intensity of radiation, which appears in the center of geometric shadow of the moon from doted source. Evaluate resolving capacity of this method, find minimal angle resolving distance for the same length of waves. Discuss a possibility of implementation of the method. Moon diameter D=3470km.

Answer 1

δφ ≈ λ/D, where λ=1 and δφ∼0,06". When λ=10cm, δφ∼0,006".
The method needs the source of radiation to be located on the straight line connecting a spot and center of the moon. Beside that it demands smooth surface and pays attention to deviation of lunar forms to spherical. The height of unevenness of the surface in all surface of lunar disk should be less than ch = bλ/D. The difference between the largest and the smallest lunar disk should not also exceed this value. When λ=1m, h∼100m; λ=10cm, h∼10m. Such demands exclude the possibility of using of the method for radio waves with the length of a wave λ<100m.