>> If I counted the number of stars in a
>> globular cluster that were resolved at the same magnification from
>> night to night, would that also be a good test of seeing?
No. The problem isn't the variable stars, but that this doesn't
test just one thing (seeing), but instead your faint magnitude threshold,
sky darkness/transparency, _and_ seeing. By being well up in brightness,
the double stars allow you to get reasonable numbers for the size of
the star image without other visual-perception difficulties getting
in the way (much).
\Brian
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