HOW SMALL A CRATER CAN WE SEE ON THE MOON? -Lew Thomas 4-28-01 First we shall apply Dawes Limit, which strictly applies to the resolution of two equally bright points of light. This is R" = 4.56/D    (1) where D = the diameter of the telescope objective in inches R" = the resolving power in seconds of arc. The mean distance of the Moon from Earth is 384,500 km. Therefore, the linear dimension of any object on its surface is R = rq    (2) where r = the distance to the Moon = 384,500 km. q = the angle of the Moon object subtended at the Earth observer in radians R = the linear dimension of the Moon object in km. Combining (1) and (2), we have R = r 4.56p/(3600x180 D) R = 8.5003/D    (3) Using this relationship and assuming a perfect telescope, the following table is constructed
 OBJECTIVE DIAMETER MINIMUM DISCERNABLE CRATER INCHES KILOMETERS Unaided eye (0.1 in.) 85 4 2.12 6 1.42 8 1.01 10 0.85 20 0.43 100 0.09 200 0.04

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