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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Lunars
From: Bill B
Date: 2005 Dec 5, 17:32 -0500
From: Bill B
Date: 2005 Dec 5, 17:32 -0500
> 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