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    Re: Meridian passage of moon
    From: Stephen N.G. Davies
    Date: 2016 Apr 13, 10:41 +0800
    Well, one possible reason may be that in remote parts of the world still relying on 19th century surveying, some errant data depends on the use of the upper and lower meridian passage of the moon. This is particularly the case for predicting the change of tidal streams in the Lombok Strait in Indonesia, with which I wrestled mightily devising ways of helping people sort things out in my and my partner’s Cruising Guide to South East Asia, vol.2. 

    As Frank says, these days most of the time most places who cares.

    Dr Stephen Davies
    c/o Department of Real Estate and Construction
    EH103, Eliot Hall
    University of Hong Kong

    Office: (852) 2219 4089
    Mobile: (852) 6683 3754 


    On 11 Apr, 2016, at 10:33 pm, Frank Reed <NoReply_FrankReed@fer3.com> wrote:

    This comes up on a regular basis. My thoughts:

    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 the moon's 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
    Conanicut Island USA

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