NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Greg Rudzinski
Date: 2011 Jul 13, 19:29 -0700
The recent discussions on time sights had me reviewing Bowditch table 25 in my 1981 vol. 2 . I was amazed to discover that table 25 not only solved for the prime vertical altitude / meridian angle but could also be used to solve for sunrise and sunset. To derive sunset it is necessary to take the complement of the latitude (90*- Lat) then re-enter table 25 using the complement as the latitude with the same declination. The (t) value will be sunrise when converted to time. Sunset will be 24:00 minus sunrise. To get exact times that match the Nautical Almanac it is necessary to adjust for the equation of time, semi-diameter, and refraction. These corrections cause an asymmetry relative to 12:00 noon which varies throughout the year. All this is new for me since I always took the tabular values in the Nautical Almanac for granted.
Greg Rudzinski
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