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Variation in tides



 
 
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  #1  
Old July 6th 06, 06:44 AM posted to uk.sci.astronomy
n cook
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Posts: 21
Default Variation in tides

According to a local old sea dog, there is a 50 year cycle to the height of
tides superimposed on the usual new/full moon / sun distance, cyclic
variation.
If there is indeed such an influence , would any one know what it is -
earth's precession ?


  #2  
Old July 6th 06, 09:28 AM posted to uk.sci.astronomy
Colin Dawson
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Posts: 4
Default Variation in tides

It's not the earth's precession, that has a cycle of about 26000 years. (I
think)

Regards

Colin Dawson
www.cjdawson.com

"n cook" wrote in message
...
According to a local old sea dog, there is a 50 year cycle to the height
of
tides superimposed on the usual new/full moon / sun distance, cyclic
variation.
If there is indeed such an influence , would any one know what it is -
earth's precession ?




  #3  
Old July 6th 06, 09:50 AM posted to uk.sci.astronomy
p forsdick
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Posts: 11
Default Variation in tides

Hello
This has prompted a question I have not worked out the answer but is
probably a very easy one and everybody else probably knows the answer.
If the moon goes round the earth once about 25 hours and is the main effect
on the tides why do we get 2 high tides in 25 hours and not one
regards Paul
"n cook" wrote in message
...
According to a local old sea dog, there is a 50 year cycle to the height
of
tides superimposed on the usual new/full moon / sun distance, cyclic
variation.
If there is indeed such an influence , would any one know what it is -
earth's precession ?




  #4  
Old July 6th 06, 10:03 AM posted to uk.sci.astronomy
n cook
external usenet poster
 
Posts: 21
Default Variation in tides

p forsdick wrote in message
. uk...
Hello
This has prompted a question I have not worked out the answer but is
probably a very easy one and everybody else probably knows the answer.
If the moon goes round the earth once about 25 hours and is the main

effect
on the tides why do we get 2 high tides in 25 hours and not one
regards Paul
"n cook" wrote in message
...
According to a local old sea dog, there is a 50 year cycle to the height
of
tides superimposed on the usual new/full moon / sun distance, cyclic
variation.
If there is indeed such an influence , would any one know what it is -
earth's precession ?





Tidal effects not travelling at 1000 mph (1000 times 24 = earth
circumference) is probably something to do with that effect


  #5  
Old July 6th 06, 11:43 AM posted to uk.sci.astronomy
Roger Hamlett
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Posts: 155
Default Variation in tides


"p forsdick" wrote in message
. uk...
Hello
This has prompted a question I have not worked out the answer but is
probably a very easy one and everybody else probably knows the answer.
If the moon goes round the earth once about 25 hours and is the main
effect on the tides why do we get 2 high tides in 25 hours and not one
regards Paul

It is wrong to think of the tides as being caused by the Moon 'pulling'.
The key is that the whole 'Earth-Moon' system, is orbiting around their
common mass centre (actually inside the Earth). In it's simplest form, the
bit of the Earth closest to the Moon, gets pulled more, and bulges upwards
towards the Moon, but at the same time, the part furthest away, gets
pulled less, and with the centripetal effect, bulges up in the opposite
direction. Worse, the actual 'tides', lag the pull, and can get
accelerated/decelerated by the local geography, so (for example), there
are places that actually get four tides (or more!) a day, as the water
takes different routes round the local land masses.

Best Wishes


  #6  
Old July 6th 06, 08:35 PM posted to uk.sci.astronomy
Robert Geake
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Posts: 9
Default Variation in tides

"n cook" wrote in message
...
According to a local old sea dog, there is a 50 year cycle to the height

of
tides superimposed on the usual new/full moon / sun distance, cyclic
variation.
If there is indeed such an influence , would any one know what it is -
earth's precession ?



A good reference::

http://home.hiwaay.net/~krcool/Astro/moon/moontides/



  #7  
Old July 6th 06, 08:36 PM posted to uk.sci.astronomy
Robert Geake
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Posts: 9
Default Variation in tides

"Roger Hamlett" wrote in message
...

"p forsdick" wrote in message
. uk...
Hello
This has prompted a question I have not worked out the answer but is
probably a very easy one and everybody else probably knows the answer.
If the moon goes round the earth once about 25 hours and is the main
effect on the tides why do we get 2 high tides in 25 hours and not one
regards Paul

It is wrong to think of the tides as being caused by the Moon 'pulling'.
The key is that the whole 'Earth-Moon' system, is orbiting around their
common mass centre (actually inside the Earth). In it's simplest form, the
bit of the Earth closest to the Moon, gets pulled more, and bulges upwards
towards the Moon, but at the same time, the part furthest away, gets
pulled less, and with the centripetal effect, bulges up in the opposite
direction. Worse, the actual 'tides', lag the pull, and can get
accelerated/decelerated by the local geography, so (for example), there
are places that actually get four tides (or more!) a day, as the water
takes different routes round the local land masses.

Best Wishes



Damn it!

The first message i actually had an accurate answer to and someone beat me
to it ):


  #8  
Old July 6th 06, 09:29 PM posted to uk.sci.astronomy
Roger Hamlett
external usenet poster
 
Posts: 155
Default Variation in tides


"Robert Geake" wrote in message
...
"Roger Hamlett" wrote in message
...

"p forsdick" wrote in message
. uk...
Hello
This has prompted a question I have not worked out the answer but is
probably a very easy one and everybody else probably knows the
answer.
If the moon goes round the earth once about 25 hours and is the main
effect on the tides why do we get 2 high tides in 25 hours and not
one
regards Paul

It is wrong to think of the tides as being caused by the Moon
'pulling'.
The key is that the whole 'Earth-Moon' system, is orbiting around their
common mass centre (actually inside the Earth). In it's simplest form,
the
bit of the Earth closest to the Moon, gets pulled more, and bulges
upwards
towards the Moon, but at the same time, the part furthest away, gets
pulled less, and with the centripetal effect, bulges up in the opposite
direction. Worse, the actual 'tides', lag the pull, and can get
accelerated/decelerated by the local geography, so (for example), there
are places that actually get four tides (or more!) a day, as the water
takes different routes round the local land masses.

Best Wishes



Damn it!

The first message i actually had an accurate answer to and someone beat
me
to it ):

Your reference, was much more complete though. :-)

Best Wishes


  #9  
Old July 6th 06, 10:15 PM posted to uk.sci.astronomy
Dr John Stockton
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Posts: 52
Default Variation in tides

JRS: In article , dated Thu, 6 Jul 2006
06:44:04 remote, seen in news:uk.sci.astronomy, n cook
posted :
According to a local old sea dog, there is a 50 year cycle to the height of
tides superimposed on the usual new/full moon / sun distance, cyclic
variation.
If there is indeed such an influence , would any one know what it is -
earth's precession ?


Never heard of it; and if it existed I'd have expected to have done so.

It seems unlikely that it's the 260th harmonic of the Earth's
precession, or the third sub-harmonic of the Metonic cycle, or the
Jubilee cycle.


Paul Forsdick : see Tides then Sea-Tides, indexed at the top of
URL:http://www.merlyn.demon.co.uk/gravity0.htm.

--
© John Stockton, Surrey, UK. Turnpike v4.00 MIME. ©
Web URL:http://www.merlyn.demon.co.uk/ - FAQqish topics, acronyms & links;
Astro stuff via astron-1.htm, gravity0.htm ; quotings.htm, pascal.htm, etc.
No Encoding. Quotes before replies. Snip well. Write clearly. Don't Mail News.
  #10  
Old July 6th 06, 11:04 PM posted to uk.sci.astronomy
Stephen Tonkin[_1_]
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Posts: 4
Default Variation in tides

p forsdick wrote:
If the moon goes round the earth once about 25 hours and is the main
effect on the tides why do we get 2 high tides in 25 hours and not one


http://astunit.com/tutorials/tides.htm

Best,
Stephen

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