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Of moon and tides



 
 
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  #11  
Old February 5th 18, 02:48 PM posted to uk.sci.astronomy
N_Cook
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Posts: 86
Default Of moon and tides

On 05/02/2018 11:52, Andy Walker wrote:
On 31/01/18 14:16, N_Cook wrote:
A quirk of celestial mechanics.

[...]
The high tides [...].


Nothing directly to do with this [interesting] discussion,
but the BBC's programme on the supermoon was trying to explain what
was meant by full/new/quarter Moon, why some were "super", etc.,
the usual stuff. In the middle of which they told us that when the
Moon was new, its pull reinforced that of the Sun, and we had higher
tides than usual. Nothing said directly, but any normal listener
would have inferred that when it was full, and its pull was opposed
to that of the Sun, tides would be lower. I've heard physicists,
who really should know better, say exactly that on TV.

In trying to explain this to people, they can usually accept
that we get "spring" tides when the Moon-tide and the Sun-tide are
reinforcing each other, and "neap" tides when they oppose. The hard
part is explaining why the Moon-tide bulges both towards and away
from the Moon. You can explain till you're blue in the face that the
Moon's gravity pull is stronger on the side of Earth facing the Moon
and weaker on the side facing away, so the water piles up [a little!]
on both sides, but somehow that gets confused with ellipses with the
Earth at one focus, and/or with the phase of the Moon.

I had one former colleague, a highly intelligent and competent
pure mathematician, who came to me regularly to explain this. "We
did this last year!" "Yes, but I've forgotten, and the children have
asked again, and anyway [famous name] was on TV and his explanation
was different. Surely we get lower high tides at full Moon?" "No,
because [blah]." "No, you've lost me. Are you saying that [name]
was wrong?" "Yes. Let's try again ...."


Brian Cox did an excellent visual-aided correct explanation of why
springs occur at new and full moons, and tidal "bulge" on opposite sides
of the Earth at any one time. A few months back on BBC something,
perhaps on Utube if not replayer.
Something to do with momentum/centrepetal forces I seem to remember
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  #12  
Old February 5th 18, 03:42 PM posted to uk.sci.astronomy
N_Cook
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Posts: 86
Default Of moon and tides

No mention of any odd tidal or moon effects in the national Times
newspaper of 03 Mar 1866 or 05 Mar 1866 , nor a local Southampton weekly
newspaper but 1/3 of it was near enough illegible.
The weekly Hampshire Chronicle i'll look in , sometime.




  #13  
Old February 5th 18, 03:46 PM posted to uk.sci.astronomy
N_Cook
external usenet poster
 
Posts: 86
Default Of moon and tides

On 05/02/2018 15:42, N_Cook wrote:
No mention of any odd tidal or moon effects in the national Times
newspaper of 03 Mar 1866 or 05 Mar 1866 , nor a local Southampton weekly
newspaper but 1/3 of it was near enough illegible.
The weekly Hampshire Chronicle i'll look in , sometime.





Just realised I looked at the wrong dates, should have been the week of
31 March 1866
  #14  
Old February 5th 18, 07:22 PM posted to uk.sci.astronomy
N_Cook
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Posts: 86
Default Of moon and tides

On 05/02/2018 11:52, Andy Walker wrote:
On 31/01/18 14:16, N_Cook wrote:
A quirk of celestial mechanics.

[...]
The high tides [...].


Nothing directly to do with this [interesting] discussion,
but the BBC's programme on the supermoon was trying to explain what
was meant by full/new/quarter Moon, why some were "super", etc.,
the usual stuff. In the middle of which they told us that when the
Moon was new, its pull reinforced that of the Sun, and we had higher
tides than usual. Nothing said directly, but any normal listener
would have inferred that when it was full, and its pull was opposed
to that of the Sun, tides would be lower. I've heard physicists,
who really should know better, say exactly that on TV.

In trying to explain this to people, they can usually accept
that we get "spring" tides when the Moon-tide and the Sun-tide are
reinforcing each other, and "neap" tides when they oppose. The hard
part is explaining why the Moon-tide bulges both towards and away
from the Moon. You can explain till you're blue in the face that the
Moon's gravity pull is stronger on the side of Earth facing the Moon
and weaker on the side facing away, so the water piles up [a little!]
on both sides, but somehow that gets confused with ellipses with the
Earth at one focus, and/or with the phase of the Moon.

I had one former colleague, a highly intelligent and competent
pure mathematician, who came to me regularly to explain this. "We
did this last year!" "Yes, but I've forgotten, and the children have
asked again, and anyway [famous name] was on TV and his explanation
was different. Surely we get lower high tides at full Moon?" "No,
because [blah]." "No, you've lost me. Are you saying that [name]
was wrong?" "Yes. Let's try again ...."


I'm not in a situation to look at videos at the moment, but this may be
the mini presentation I saw
http://www.youtube.com/watch?v=WGKgKayuC2M

  #15  
Old February 5th 18, 07:34 PM posted to uk.sci.astronomy
Andy Walker[_3_]
external usenet poster
 
Posts: 2
Default Of moon and tides

On 05/02/18 14:48, N_Cook wrote:
Brian Cox did an excellent visual-aided correct explanation of why
springs occur at new and full moons, and tidal "bulge" on opposite
sides of the Earth at any one time. A few months back on BBC
something, perhaps on Utube if not replayer.


Perhaps "Forces of Nature"? See

https://www.youtube.com/watch?v=4UZxzyOVJ8Q

He has a somewhat different version from "Stargazing" at

https://www.youtube.com/watch?v=WGKgKayuC2M [1]

and I expect there are others. Neither of these really explains
spring/neap, though, AFAIR, nor why the Moon is more important
than the Sun for this purpose.

Something to do with momentum/centrepetal forces I seem to remember


On the other hand, for whether he is correct, people should
perhaps look at the first half of

https://www.youtube.com/watch?v=pwChk4S99i4

Food for thought!

[1] Just seen your other article! But I'll let this one stand anyway.

--
Andy Walker,
Nottingham.
  #16  
Old February 6th 18, 02:25 PM posted to uk.sci.astronomy
Martin Brown[_3_]
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Posts: 111
Default Of moon and tides

On 05/02/2018 14:44, N_Cook wrote:
On 05/02/2018 09:01, Martin Brown wrote:


My email address is valid so if you would be kind enough to your NOC
expert to get in touch I would be interested to discuss with them why
they would dismiss the possibility of tidal forcing out of hand.


I'll tell him of your recent post and "newspam"@... em address,

remove both " ?

Make absolutely no changes and it should get through unmolested.

Spammers scripts can't resist removing "spam" from it or correcting the
number of '''. In a previous incarnation it used "|" which really messed
up poorly designed Unix spammers scripts.

My new mailserver doesn't allow the use of the pipe character.

My interest is a bit more parochial.
I wonder if the "sotonisation" of the pompey tides

https://www.admiralty.co.uk/Admiralt...20stan ds.pdf
and multiple high-waters for Soton also since the end of 2015,
(correspondence with Southampton Hydrographic office confirming this

phenomenom but no insight as to cause, from them)
change in Lymington tide times, growth of a spit at Pagham Harbour

are all connected.
Perhaps connected to whatever tidal harmonic constituents are close

to syncing together for 2 or more years , along with the
super-blue-blood moon, and all these local effects might drop out again
after 2 more years.

Myself and 3 proper NOC oceanographers are intrigued about this local

effect, so far tentatively "blamed" on dredging for aggregates in the
English channel, but an astronomic cause is much more interesting.

Worth taking a look at the times series for likely candidates. Eclipses
are a crude proxy for good alignment the ones around now close to
perigee can do the most thrashing with the moon at its closest.

To turn a sine wave into a square wave you are looking for a third
harmonic component in antiphase and 1/3 the amplitude (or to just get a
flattish top (2n+1)th harmonic and the right amplitude to match).

Accidentally sent this to your email address and just noticed the
bounce... sorry for the delay (and mangled formatting).

--
Regards,
Martin Brown
 




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