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 DIAMETERMINIMUM 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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Page last updated 06/12/2001