Probably stupid question

[benjenbav]

Looking at the excellent pix of the big spring tide at Portishead http://www.ybw.com/forums/showthread.php?t=230242 I started wondering if, on a day when it's springs in UK, it is also springs everywhere else. Or is it maybe neaps in Oz?

 

[jhr]

I think the strength of the tides is to do with the relative positions of the Moon, the Sun and the Earth, innit? So I'm guessing that when it's springs here, it's springs everywhere.

 

[benjenbav]

That's what I thought but then I started wondering whether the difference in the relative positions of earth, sun and moon was less than the difference between one side of the world and the other and so maybe when the moon's gravitational force is turned up to 10 for the UK it might be on 1 for Australia, if you see what I mean.

 

[jimg]

As you can see the moon phase is "reversed"

UK
http://www.dacre.net/moon/moonphase.html

OZ
http://moonphases.willyweather.com.au/nsw/sydney/bondi-beach.html

So I guess they have springs at the same time as us. (The next full moon is March 30 in both places)

 

[BartW]

That's what I thought but then I started wondering whether the difference in the relative positions of earth, sun and moon was less than the difference between one side of the world and the other and so maybe when the moon's gravitational force is turned up to 10 for the UK it might be on 1 for Australia, if you see what I mean.

I think that springs (or neaps) is all over the earth (within a phase shift of 24hrs)
basically if you have high tide at your place, it is also high tide on the opposite side of the earth, yes I know, this is difficult to believe and even more difficult to explain,
Why else do you have a tide change approx every 6hr's and not every 12hr's ?

 

[ExcaliburII]

I think springs and neaps occurs at broadly the same time of the (lunar) month all over the Earth.

I can remember as a youngster (I'm going way, way back now ) my father commenting on more than one occasion that it must be a spring tide because high water was about 8pm. It was only when I did my Day Skipper course (long after Dad had passed away) I found out that, whilst this is true in the Bristol Channel, it's not the case everywhere. I haven't done the detailed research, but I suspect that spring tides at any given place will always occur at the same time of day, albeit at different times at different places.

 

[Searush]

I think springs and neaps occurs at broadly the same time of the (lunar) month all over the Earth.

I can remember as a youngster (I'm going way, way back now ) my father commenting on more than one occasion that it must be a spring tide because high water was about 8pm. It was only when I did my Day Skipper course (long after Dad had passed away) I found out that, whilst this is true in the Bristol Channel, it's not the case everywhere. I haven't done the detailed research, but I suspect that spring tides at any given place will always occur at the same time of day, albeit at different times at different places.

Correct, in fact, if you read pilot notes from 100 years ago or so (eg the Frank Cowper circumnav books) you will find that tides at each port/ anchorage are defined as the time of High water springs (Full & Change is the phrase used to identify full moon & no moon). The data is as true today as it was in the 1850's & allows a full tide table to be calculated - given some local discrepancies caused by narrow channels/ entrances.