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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Parallactic retardation - don't give up so easily.
From: Frank Reed CT
Date: 2004 Jan 9, 18:00 EST
From: Frank Reed CT
Date: 2004 Jan 9, 18:00 EST
Bruce Stark wrote:
"Actually I hope I'm wrong in this, as some people might feel constrained to take lunars only at "appropriate" times."
This all gets back to the question of why people would want to shoot lunars in the first place. There will be a wide spectrum of reasons based on issues like historical recreation, challenge of sextant handling, mathematical curiosity, bragging rights, and even post-apocalypse navigation for some (I would be interested in any others).
And:
"And experience suggests I am wrong. Seems to me the lunars I've taken when the moon is on or near the meridian have been as good or better than average."
It really is mostly a question of the Moon's altitude. Try some experiments. If you don't want to work large numbers of experiments by hand, use Arthur Pearson's lunar distance spreadsheet or my online calculator (at http://www.clockwk.com/cell/lunars_xx.html with explanation at /cell/aboutlun.html) and see how the GMT of the sight changes when you increment the observed lunar distance by some fixed error amount (e.g. 0.2 minutes of arc).
Frank E. Reed
[X] Mystic, Connecticut
[ ] Chicago, Illinois
"Actually I hope I'm wrong in this, as some people might feel constrained to take lunars only at "appropriate" times."
This all gets back to the question of why people would want to shoot lunars in the first place. There will be a wide spectrum of reasons based on issues like historical recreation, challenge of sextant handling, mathematical curiosity, bragging rights, and even post-apocalypse navigation for some (I would be interested in any others).
And:
"And experience suggests I am wrong. Seems to me the lunars I've taken when the moon is on or near the meridian have been as good or better than average."
It really is mostly a question of the Moon's altitude. Try some experiments. If you don't want to work large numbers of experiments by hand, use Arthur Pearson's lunar distance spreadsheet or my online calculator (at http://www.clockwk.com/cell/lunars_xx.html with explanation at /cell/aboutlun.html) and see how the GMT of the sight changes when you increment the observed lunar distance by some fixed error amount (e.g. 0.2 minutes of arc).
Frank E. Reed
[X] Mystic, Connecticut
[ ] Chicago, Illinois
