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Sorry, we don't have any Tidal Clock and How Tide Clocks Work to feature at the moment. Please check back another time. Meanwile here's some interesting information. Whatever your relationship with the sea, it is always important and useful to know the current position of the tide. Buy one of these tidal clocks for yourself or as a gift to someone who enjoys sailing, fishing or simply being near the sea, and you'll be getting something that will be useful for many years to come.
How does a tide clock work?
Due to the fact that the gravitational pull of the moon on the oceans is the major influence on the tides, tidal clocks work by timing the aparent motion of the moon around the earth. The actual true orbit of the moon takes 29 days, 12 hours, 44 minutes and 2.8 seconds, (ie 29.53 days) but as the earth is spinning on its own axis too, the moon appears to rise and set every day as the earth turns, in a similar way to how the sun appears to rise and set every day. The direction of the moon's actual 29.53 day cycle around the earth is the same direction as the turn of the earth''s axis. Therefore by the time the earth has turned once on its axis (which takes 24 hours), the moon has advanced around the earth a little. The advance of the moon in one day is 1/ 29.53 of its full cycle. The planet earth must therefore rotate for another 1/29.53 of a day (48.76 minutes) to arrive at where the moon was after the earth's initial 24 hour turn. You can take this further by realising that after these extra 48.76 minutes of the earth's travel, the moon has again moved forward a little more, but we're now getting into such exact figures that become slightly inappropriate when talking about the tide, as, although it the sun's influence is much less than that of the moon when it comes to tidal flow, the position of the sun does also have a small influence on the tidal flows.
The sun's effect on the timing of tides is greates at times of the last quarter and first quarter of the moon. At this point the moon and sun are at right angles to each other when viewed from earth. This causes the high tides to be lower than usual, and low tides to be higher than usual, and can cause differences of up to half an hour in expected high and low tide times.
Effectively then, we're talking about a period of around 24 hours 48.7 minutes between the moon appearing in the same part of our sky when viewed from earth. At first thought it would appear that this would give only one high tide per day, but in most areas there are actually two high tides and two low tides each day. This is due to the effects of gravitation on the solid body of the planet earth, and also the effect of centrifugal forces.
The earth and moon actually have a combined centre of gravity around which both planetary objects circle. This center of gravity is not out there in space between the two bodies, but is actually inside the earth, as a result of the earth's much larger mass than the moon. This center of gravity, which is always in the direction of the moon, and the earth wobbles around this center, meaning that the side of the earth furthest away from the moon experiences a centrifugal force which pushes the liquid water of the seas outward. This effect is combined with the fact that the gravitational pull of the moon pulls the solid body of the earth, including the sea floor on the opposite side of the moon, toward the moon itself. The elipse of water, being liquid rather than a solid mass, is therefore higher on both the side closest and furthest to the moon.
With two tides in one apparent orbit of the moon around the earth, and a period of 24 hours 48.7 minutes for each of these orbits, this gives a perion of around 12 hours 24 minutes between successive high tides. This is the time that it takes for tidal clocks to complete one rotation of their tide hand from one high tide to the next. On the opposite side of the high tide indicator, there is a low tide indicator, and most clocks also show a count-down style of "hours until high tide" and "hours until low tide". In many cases the tide clock will be combined with a normal 12 hour clock, either in an inner or outer ring of digits on the clockface. This can give you a total of up to 4 hands on the clock, which may look a little confusing at first. It's easy really though they're just the normal hour, minute and second hand which display the actual time of day, plus there's the extra hand for the tidal clock.
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