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[NavList] Moonrise on June 17-19
From: billyrem42---net
Date: 26 Jun 2011 18:40

Hello my Friend,

If her Declination were absolutely constant, from any point on Earth where visible, Lady Moon would raise every day about 24h50m (i.e. 24h + about a 50 min "delay") LATER than the previous day, simply because she keeps circling around the Earth in approximately 28 days.

However ... the Moon Declination varies sometimes greatly (up to 5° or 6° per 24 hours).

Therefore,

- if watched from North Latitudes when her Declination increases rapidly towards the North, or

- if watched from South Latitudes when her Declination increases rapidly towards the South,

the fact the the "day after" Lady Moon has come much closer from the Observer's elevated pole makes her to rise "sooner" than the day before.

And this "sooner" effect can at times more than offset the 50 min dayly "delay" mentioned hereabove. As a consequence, if you are observing from either high North or South Latitudes, there will be cases when you can observe 2 successive Moon Risings (or 2 successive Moon Settings) in less than a 24 hour time span, but definitely NOT in the same successive Azimuths.

I therefore think that this can happen only at high North or South Latitudes when the effect of changing Declinations - with its well known strongest influence close to the poles - is sufficiently "strong" to counteract the 50 minute dayly delay on the rising/setting times.

It also works the way around for setting times, again seen from high North/South Latitudes.

Best Regards

Kermit

Antoine M. "Kermit" Couëtte

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