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From: Bill (no email)
Date: Mon Dec 05 2005 - 17:32:29 EST
> Does anyone have suggestions about judging tangency?
> Any other suggestions - other than practise - to
> improve matters.
Mike
I personally find planets a bit more difficult than stars for star-to-star
and lunar distances. Mars was over 0.3' in diameter this fall, so you have
to split the planet at the edge of the moon. Many have phases like the moon
so what you see through a scope is not necessarily what you get. The 2005
almanac has additional corrections for Venus up to 0.4'. (Of course this is
on the vertical, and your shot was probably close to horizontal.) Whether
there is parallax involved I do not know. I also do not know if Frank's site
adjusts for the phase etc.
I have recently noticed the same personal error (undershooting lunars). I
had been using a neutral-density shade over the moon (Astra III B, split
horizon mirror). I found if I add anther shade (light green) It helps to
get rid of the "ring" my old eyes see around the moon. Adding a light shade
to Venus or Mars also helps reduce their apparent size for me. (Note
irradiation causes a bright object against a dark background to appear
larger--so reducing the brightness kills two birds with one stone in my
case.)
Another great tip came from Frank Reed if AI recall. I find it very
helpful, especially in "awkward" positions. Hold the sextant with both
hands. Get close and take a quick break. Look again, tweak, break, tweak.
You might also try a set-and-wait method after tweaking.
Using these two tips I find I can now consistently get get within 0.4' or
better.
Hope that helps
Bill
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