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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Maintained by Ray Shapp Page last updated 06/12/2001 |