NavList:
A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Why does the Nautical Almanac include Moon lower meridianpassage?
From: Lu Abel
Date: 2015 Jan 11, 21:05 +0000
From: Lu Abel
Date: 2015 Jan 11, 21:05 +0000
Nice explanation, Frank.
Yeah, traditions die hard, especially when there are half a dozen FREE iPhone apps that give tidal predictions for every local station (no more calculating at the reference station and then adding/subtracting time and value "offsets") Oh, wait, I still need that for the free tide books my marina gives out.
From: Frank Reed <NoReply_FrankReed@fer3.com>
To: luabel@ymail.com
Sent: Sunday, January 11, 2015 12:41 PM
Subject: [NavList] Re: Why does the Nautical Almanac include Moon lower meridianpassage?
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
