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A Community Devoted to the Preservation and Practice of Celestial Navigation and Other Methods of Traditional Wayfinding
Re: Big Full Moon and Perigee Spring Tides
From: John Huth
Date: 2011 Mar 19, 09:57 -0400
From: John Huth
Date: 2011 Mar 19, 09:57 -0400
Frank -
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Keeping up with the grind
I'm at Cape Cod today, and we do have some big tides today, so that much is interesting.
I did a bit of digging on the definition of high astronomical tide and low astronomical tide. There is a move to try to standardize this for bathymetric datum for all charts, but a) the US is still using MLLW (mean lower low water) and b) the definition of astronomical tides is a bit elusive.
In an operational definition, it seems to be the 'lowest' tide recorded over some longish time period. A more thorough definition in other countries seems to be based on the metonic cycle of 19 years. A even more thorough definition would be the earth at perihelion, the moon at perigee, the sun and moon in conjunction and both the sun and moon at zero declination, which my source tells me will next happen in 6580 AD. I don't think any country uses this definition.
Regarding the west coast panic, my cousin who lives in San Francisco e-mailed me, asking about potassium iodide tablets. I resisted the urge to reply "R U NUTS?", and instead composed a thoughtful message with all the reasons why the Daiichi problem cannot affect the US West Coast.
John H.
On Sat, Mar 19, 2011 at 5:20 AM, Frank Reed <FrankReed@historicalatlas.com> wrote:
An article from S&T about some of the exaggerated claims regarding the Full Moon today:
http://www.skyandtelescope.com/observing/home/118265299.htmlIt makes a simple, excellent point: "When it comes to science stories, if you don't know it in numbers, you don't know it at all".
There's also some good advice on "frantic aunts" forwarding brain-dead emails.
-FER
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Keeping up with the grind
