Quote:
Originally Posted by 5ash
The distance of the artificial star is of importance as the diameter of the star in arc minutes must be smaller than the resolution of your scope, after all we can't resolve a star as a disk. For this to happen the physical diameter of the artificial star must be unresolvable at the distance it is observed. For an 8" scope using a common diameter star this would be in excess of 40 metres.
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It depends on the diameter of the artificial star - and that is what makes the image of the Sun on a small ball bearing such a good artificial star.
The Sun's image on a 10 mm ball bearing at a distance of 20 metres is about 22 microns diameter (about half the size of the hole in commercial "artificial star" devices), which translates to a subtended angle of about 0.25 arc-seconds, which is below the theoretical resolution of even a 12" SCT. It is a brilliant pin-point of light, which is easily observed when the ball bearing is placed against a black card or similar.