A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Robin Stuart
Date: 2020 Jan 7, 09:08 -0800
I revisited the calculation of the northern and southern latitude limits for occultations. Blind application of the rules given in the 1836 Nautical Almanac, at least my reading of them, give some strange results. In the first file I give the modification that needs to be made to give correct results.
I also derived expressions for the limits directly in terms of Besselian element and give an explanation and formulas in the second document. The limits generated by the corrected NA methodology and the Besselian Elements agree for all of the over 3,000 possible worldwide events for 2020.
Finally I reattach the occultation calculation spreadsheet set up form Mystic previously posted here. The functionally it has not changed but it has been updated with a background data set that uses the corrected limits methodology and applies more stringent restrictions on the accepted events meaning the total number of possible events is slightly reduced.
The corrected limit calculation will not change anything for an observer in temperate latitudes compared to the previous version but occasionally there might have been the odd event missed if you happened to be observing near the poles.