HOW SMALL A SUNSPOT CAN WE SEE ON THE SUN? -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 Sun from Earth is 149,000,000 km. Therefore, the linear dimension of any object on its surface is R = rq (2) where r = the distance to the Sun = 149,000,500 km q = the angle of the Sun object subtended at the Earth observer in radians R = the linear dimension of the Sun object in km Combining (1) and (2), we have R = r 4.56p/(3600x180 D) R = 3294.18/D (3) Using this relationship and assuming a perfect telescope, the following table is constructed |
OBJECTIVE DIAMETER | MINIMUM DISCERNABLE SUNSPOT |
INCHES | KILOMETERS |
Unaided eye (0.1 in.) |
30,390 |
4 |
824 |
6 |
549 |
8 |
412 |
10 |
329 |
20 |
165 |
100 |
33 |
200 |
17 |
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Maintained by Ray Shapp Page last updated 06/12/2001 |