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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
From: Frank Reed
Date: 2015 Jan 11, 12:38 -0800
You wrote:
"Nautical Almanac right hand page has both upper and lower meridian passage for the moon. Why the lower?"
I believe it's mostly a relic of traditional tide prediction. For any port with relatively "normal" semi-diurnal (meaning twice daily) tides, there is a relatively stable offset between the Moon's meridian passage and the times of high and low high tides. For example, in Mystic, Connecticut, low tide occurs three hours after meridian passage. The same rule applies to lower meridian passage. Now of course, one can easily estimate the time of lower meridian passage. It's about 12.5 hours after upper meridian passage. A tabulated almanac value is hardly necessary. Traditions die hard.
Frank Reed
ReedNavigation.com
Conanicut Island USA
