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The tide is the regular rising and falling of the ocean's surface caused by changes in gravitational forces external to the Earth. The main changing gravitational field is due to the Moon while a lesser field is caused by the Sun. For the French ship of the line, see Océan Ocean (from Okeanos, a Greek god of sea and water; Greek ωκεανός) covers almost three quarters (71%) of the surface of the Earth. ...
This article covers the physics of gravitation. ...
Earth - Wikipedia, the free encyclopedia /**/ @import /skins-1. ...
The gravitational field is a field that causes bodies with mass to attract each other. ...
Crust composition Oxygen 43% Silicon 21% Aluminium 10% Calcium 9% Iron 9% Magnesium 5% Titanium 2% Nickel 0. ...
The Sun is the star at the centre of our Solar system. ...
Tidal terminology
 The Bay of Fundy at high tide
 The same location at low tide The maximum water level is called "high tide" or "high water" and the minimum level is "low tide" or "low water". High water occurs as two bulges in the height of the oceans; one bulge faces the moon and the other, on the opposite side of the earth, faces away from the moon. For an explanation see below under Tidal physics. There are two low waters positioned at about 90° of longitude from the high waters. The bay of Fundy at high tide This picture was taken in about 1972 by me. ...
The bay of Fundy at high tide This picture was taken in about 1972 by me. ...
The Bay of Fundy at low tide taken in 1972 File links The following pages link to this file: Tide Bay of Fundy Categories: GFDL images ...
The Bay of Fundy at low tide taken in 1972 File links The following pages link to this file: Tide Bay of Fundy Categories: GFDL images ...
Map of Earth showing curved lines of longitude Longitude, sometimes denoted λ, describes the location of a place on Earth east or west of a north-south line called the Prime Meridian. ...
At any given point on the ocean, there are normally two high tides and two low tides each day. On average, high tides occur 12 hours 24 minutes apart. The 12 hours is due to the Earth's rotation, and the 24 minutes to the Moon's orbit. The 12 hours is half of a solar day and the 24 minutes is half of a lunar extension, which is 1/(29-day lunar cycle). Earth - Wikipedia, the free encyclopedia /**/ @import /skins-1. ...
Rotation is the movement of a body in such a way that the distance between a certain fixed point and any given point of that body remains constant. ...
In physics, an orbit is the path that an object makes, around another object, whilst under the influence of a source of centripetal force, such as gravity. ...
Solar time is based on the idea that, when the sun reaches its highest point in the sky, it is noon. ...
The time between high tide and low tide, when the water level is falling, is called the "ebb". The time between low tide and high tide, when the tide is rising, is called "flow" or "flood".
The height of the high and low tides (relative to mean sea level) also varies. Around new and full Moon when the Sun, Moon and Earth form a line, the tidal forces due to the Sun reinforce those of the Moon, due to the syzygy found at those times. Diagram of lunar phases, created by Minesweeper and donated to Wikipedia. ...
Diagram of lunar phases, created by Minesweeper and donated to Wikipedia. ...
Traditionally, the lunar phase new moon begins with the first visible crescent of the Moon, after conjunction with the Sun. ...
The Galileo spacecraft took this composite image on 7 December 1992 on its way to explore the Jupiter system in 1995-97. ...
The tidal force is a secondary effect of the force of gravity and is responsible for the tides. ...
The Sun is the star at the centre of our Solar system. ...
Syzygy can refer to any of several different things: Astronomy In astronomy, a syzygy (Greek: yoked together) is a situation where three celestial bodies are positioned along a straight line. ...
The tides' range is then at its maximum: this is called the "spring tide", or just "springs" and is derived not from the season of spring but rather from the German verb springen, meaning "to leap up". When the Moon is at first quarter or third quarter, the sun and moon are at 90° to each other and the forces due to the Sun partially cancel out those of the Moon. At these points in the Lunar cycle, the tide's range is at its minimum: this is called the "neap tide", or "neaps".
Spring tides result in high waters that are higher than average, low waters that are lower than average, slack water time that is shorter than average and stronger tidal currents than average. Neaps result in less extreme tidal conditions. Normally there is a seven day interval between springs and neaps. Slack water is the time during which no appreciable current in flowing in a body of water. ...
The relative distance of the Moon from the Earth also affects tide heights: When the Moon is at perigee the range increases, and when it is at apogee the range is reduced. Every 7½ lunations, perigee and (alternately) either a new or full Moon coincide; at these times the range of tide heights is greatest of all, and if a storm happens to be moving onshore at this time, the consequences (in the form of property damage, etc.) can be especially severe (surfers are aware of this, and will often intentionally go out to sea during these times, as the waves are more spectacular than ever). The effect is enhanced even further if the line-up of the Sun, Earth and Moon is so exact that a solar or lunar eclipse occurs concomitant with perigee. This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ...
This article is about several astronomical terms (apogee & perigee, aphelion & perihelion, generic equivalents based on apsis, and related but rarer terms. ...
Lunation is the mean time for one lunar phase cycle (i. ...
Surfing outside Kaneohe Bay, Hawai‘i. ...
Photo taken by John Walker during the Zambia 2001 eclipse A solar eclipse occurs when the Sun, Moon and Earth are on a single line with the Moon in the middle. ...
An eclipse occurs whenever the Sun, Earth and Moon line up exactly. ...
Total solar eclipse in Zambia, 2001 An eclipse (Greek verb: ecleipo = cease to exist) is an astronomical event that occurs when one celestial object moves into the shadow of another. ...
Timing In most places there is a delay between the phases of the Moon and its effect on the tide. Springs and neaps in the North Sea, for example, are two days behind the new/full Moon and first/third quarter, respectively. The reason for this is that the tide originates in the southern oceans, the only place on the globe where a circumventing wave (as caused by the tidal force of the Moon) can travel unimpeded by land. The North Sea is a sea of the Atlantic Ocean, located between the coasts of Norway and Denmark in the east, the coast of the British Isles in the west, and the German, Dutch, Belgian and French coasts in the south. ...
The resulting effect on the amplitude, or height, of the tide travels across the oceans. It is known that it travels as a single broad wave pulse northwards over the Atlantic. This causes relatively low tidal ranges in some locations (nodes) and high ones in other places. This is not to be confused with tidal ranges caused by local geography, as can be found in Nova Scotia, Bristol, the Channel Islands, and the English Channel. In these places tidal ranges can be over 10 metres. The Atlantic Ocean is Earths second-largest ocean, covering approximately one_fifth of its surface. ...
The term node can refer to: Node, a spatial locus along a standing wave where the wave has minimal amplitude. ...
Motto: Munit Haec et Altera Vincit (One defends and the other conquers) Other Canadian provinces and territories Capital Halifax Largest city Halifax Lieutenant Governor Myra A. Freeman Premier John Hamm (PC) Area 55,283 km² (12th) - Land 53,338 km² - Water 1,946 km² (3. ...
Bristol is an English city and county and one of the two administrative centres of South West England (the other being Plymouth). ...
The Channel Islands are a group of islands off the coast of Normandy, France, in the English Channel. ...
The English Channel (French: La Manche, the sleeve) is the part of the Atlantic Ocean that separates the island of Great Britain from northern France, and joins the North Sea to the Atlantic Ocean. ...
The Atlantic tidal wave arrives after approximately a day in the English Channel area of the European coast and needs another day to go around the British Isles in order to have an effect in the North Sea. Peaks and lows of the Channel wave and North Sea wave meet in the Strait of Dover at about the same time but generally favour a current in the direction of the North Sea. Europe - Wikipedia, the free encyclopedia /**/ @import /skins-1. ...
The British Isles consist of Great Britain, Ireland and a number of much smaller surrounding islands. ...
Satellite image of the Strait of Dover The Strait of Dover (Fr. ...
The exact time and height of the tide at a particular coastal point is also greatly influenced by the local topography. There are some extreme cases: the Bay of Fundy, on the east coast of Canada, features the largest well-documented tidal ranges in the world, 16 metres (53 feet), because of the shape of the bay. Southampton in the United Kingdom has a double high tide caused by the flow of water around the Isle of Wight, and Weymouth, Dorset has a double low tide because of the Isle of Portland. Ungava Bay in Nunavut, north eastern Canada, is believed by some experts to have higher tidal ranges than the Bay of Fundy (about 17 metres or 56 feet), but it is free of pack ice for only about four months every year, whereas the Bay of Fundy rarely freezes even in the winter. A coastal image featured on a United States postal stamp. ...
Surface of the Earth Topography, a term in geography, has come to refer to the lay of the land, or the physiogeographic characteristics of land in terms of elevation, slope, and orientation. ...
The Bay of Fundy is a bay located on the Atlantic coast of North America, on the northeast end of the Gulf of Maine between the provinces of New Brunswick and Nova Scotia. ...
Civic Centre, Southampton Southampton is a city and major port situated on the south coast of England. ...
The Isle of Wight is an island off the south coast of England, opposite Southampton popularized from Victorian times as a holiday resort. ...
Weymouth Promenade in 1993 Weymouth is a coastal town in Dorset, England. ...
Chesil Beach from the hill above Fortuneswell, Portland Harbour is on the right. ...
Ungava Bay is a large bay in northeastern Canada separating Nunavik (far northern Québec) from Baffin Island. ...
Motto: Nunavut Sannginivut (Inuktitut, Nunavut our strength / Our land our strength) Other Canadian provinces and territories Capital Iqaluit Largest city Iqaluit Commissioner Ann Meekitjuk Hanson Premier Paul Okalik (independent) Area 2,093,190 km² (1st) - Land 1,936,113 km² - Water 157,077 km² (7. ...
The Bay of Fundy is a bay located on the Atlantic coast of North America, on the northeast end of the Gulf of Maine between the provinces of New Brunswick and Nova Scotia. ...
An icebreaker navigates some through young (1 year) sea ice Sea ice is formed from ocean water that freezes. ...
There are only very slight tides in the Mediterranean Sea and the Baltic Sea due to their narrow connections with the Atlantic Ocean. Extremely small tides also occur for the same reason in the Gulf of Mexico and Sea of Japan. On the southern coast of Australia, because the coast is extremely straight (partly due to the tiny quantities of runoff flowing from rivers), tidal ranges are equally small. Satellite image Map of the Mediterranean Sea The Mediterranean Sea is a part of the Atlantic Ocean almost completely enclosed by land, on the north by Europe, on the south by Africa, and on the east by Asia. ...
The Baltic Sea is located in Northern Europe, bounded by the Scandinavian Peninsula, the mainlands of Northern Europe, Eastern Europe, Central Europe, and the Danish islands. ...
The Gulf of Mexico is a major body of water bordered and nearly landlocked by North America. ...
The Sea of Japan (In South Korea, it is known as East Sea and in North Korea as East Sea of Korea) is a marginal sea of the western Pacific Ocean, bound by the Japanese islands of Hokkaido, Honshu, and Kyushu and the Russian island of Sakhalin to the east...
Run-off, composed of a mixture of water and soil along with any other organic or inorganic substances that may exist in the land, is the product of precipitation, snowmelt, over-irrigation, or other water coming in contact with the earth and carrying matter to streams, rivers, lakes, and other...
Tidal physics Ignoring external forces, the ocean's surface defines a geopotential surface or geoid, where the gravitational force is directly towards the centre of the Earth and there is no net lateral force and hence no flow of water. The GOCE project will measure high-accuracy gravity gradients and provide an accurate geoid model based on the Earths gravity field. ...
Now consider the effect of added external, massive bodies such as the Moon and Sun. These massive bodies have strong gravitational fields that diminish with distance in space. It is the spatial differences in these fields that deform the geoid shape. This deformation has a fixed orientation relative to the influencing body and the rotation of the Earth relative to this shape drives the tides around. Gravitational forces follow the inverse-square law (force is inversely proportional to the square of the distance), but tidal forces are inversely proportional to the cube of the distance. The Sun's gravitational pull on Earth is 179 times bigger than the Moon's, but because of its much greater distance, the Sun's tidal effect is smaller than the Moon's (about 46% as strong). For simplicity, the next few sections use the word "Moon" where also "Sun" can be understood. This diagram shows how the law works. ...
In algebra, the square of x is written x2 and is defined as the product of x with itself: x × x. ...
In arithmetic and algebra, the cube of a number n is its third power — the result of multiplying it by itself two times: n3 = n × n × n. ...
Since the Earth's crust is solid, it moves with everything inside as one whole, as defined by the average force on it. For a geoid shape this average force is equal to the force on its centre. The water at the surface is free to move following forces on its particles. It is the difference between the forces at the Earth's centre and surface which determine the effective tidal force.
At the point right "under" the Moon (the sub-lunar point), the water is closer than the solid Earth; so it is pulled more and rises. On the opposite side of the Earth, facing away from the Moon (the antipodal point), the water is farther than the solid earth, so it is pulled less and moves away from Earth, rising as well. On the lateral sides, the water is pulled in a slightly different direction than at the centre. The vectorial difference with the force at the centre points almost straight inwards to Earth. It can be shown that the forces at the sub-lunar and antipodal points are approximately equal and that the inward forces at the sides are about half that size. Somewhere in between there is a point where the tidal force is parallel to the Earth's surface. Those parallel components actually contribute most to the formation of tides, since the water particles are free to follow. The actual force on a particle is only about a ten millionth of the force caused by the Earth's gravity.
These minute forces all work together:
- pull up under and away from the Moon
- pull down at the sides
- pull towards the sub-lunar and antipodal points at intermediate points
So two bulges are formed pointing towards the Moon just under it and away from it on Earth's far side.
Tidal amplitude and cycle time Since the Earth rotates relative to the Moon in one lunar day (24 hours, 48 minutes), each of the two bulges travels around at that speed, leading to one high tide every 12 hours and 24 minutes. The theoretical amplitude of oceanic tides due to the Moon is about 54 cm at the highest point. This is the amplitude that would be reached if the ocean were uniform with no landmasses and Earth not rotating. In space exploration, a lunar day is the period of time it takes for the Moon to complete one full rotation on its axis. ...
The Sun similarly causes tides, of which the theoretical amplitude is about 25 cm (46 % of that of the Moon) and the cycle time is 12 hours.
At spring tide the two effects add to each other to a theoretical level of 79 cm, while at neap tide the theoretical level is reduced to 29 cm.
Real amplitudes differ considerably, not only because of global topography as explained above, but also because the natural period of the oceans is in the same order of magnitude as the rotation period: about 30 hours (by comparison, the natural period of the Earth's crust is about 57 minutes). This means that, if the Moon suddenly vanished, the level of the oceans would oscillate with a period of 30 hours with a slowly decreasing amplitude while dissipating the stored energy. This 30 h value is a simple function of terrestrial gravity and the average depth of the oceans.
The distances of Earth from the Moon or the Sun vary, because the orbits are not circular, but elliptical. This causes a variation in the tidal force and theoretical amplitude of about ±18% for the Moon and ±5% for the Sun. So if both are in closest position and aligned, the theoretical amplitude would reach 93 cm.
Tidal lag Because the Moon's tidal forces drive the oceans with a period of about 12.42 hours (half of the Earth's synodic period of rotation), which is considerably less than the natural period of the oceans, complex resonance phenomena take place. The lag between the Moon's passage and the tidal response varies between 2 hours in the southern oceans, to two days in the North Sea. The global average tidal lag is six hours (which means low tide occurs when the Moon is at its zenith or its nadir, a result that goes against common intuition). Tidal lag and the transfer of momentum between sea and land causes the Earth's rotation to slow down and the Moon to be moved further away in a process known as tidal acceleration. The North Sea is a sea of the Atlantic Ocean, located between the coasts of Norway and Denmark in the east, the coast of the British Isles in the west, and the German, Dutch, Belgian and French coasts in the south. ...
The tidal acceleration of the Moon is a peculiar effect in the dynamics of the Earth-Moon system, that has important long-term consequences for the orbit of the Moon and the rotation of the Earth. ...
Alternative explanation Some other explanations in articles on the physics of tides include the (apparent) centrifugal force on the Earth in its orbit around the common centre of mass (the barycentre) with the Moon. The barycentre is located at about ¾ of the radius from the Earth's centre. It is important to note that the Earth has no "rotation" around this point. It just "displaces" around this point in a circular way. Every point on Earth has the same angular velocity and the same radius of orbit, but with a displaced centre. So the centrifugal force is uniform and does not contribute to the tides. However, this uniform centrifugal force is just equal (but with opposite sign) to the gravitational force acting on the centre of mass of Earth. So subtracting the gravitational force at the centre of Earth from the local gravitational forces at the surface, has the same effect as adding the (uniform) centrifugal forces. Although these two explanations seem very different, they yield the same results. The barycenter (from the Greek βαρύκεντρον) is the center of mass of two or more bodies which are orbiting each other, and is the point around which both of them orbit. ...
Tides and navigation Tidal flows are of profound importance in navigation and very significant errors in position will occur if tides are not taken into account. Tidal heights are also very important; for example many rivers and harbours have a shallow "bar" at the entrance which will prevent boats with significant draught from entering at certain states of the tide.
Tidal flow can be found by looking at a tidal chart or tidal stream atlas for the area of interest. Tidal charts come in sets, each one of the set covering a single hour between one high tide and another (they ignore the extra 24 minutes) and give the average tidal flow for that one hour. An arrow on the tidal chart indicates direction and two numbers are given: average flow (usually in knots) for spring tides and neap tides respectively. If a tidal chart is not available, most nautical charts have "tidal diamonds" which relate specific points on the chart to a table of data giving direction and speed of tidal flow. Standard procedure is to calculate a "dead reckoning" position (or DR) from distance and direction of travel and mark this on the chart (with a vertical cross like a plus sign) and then draw in a line from the DR in the direction of the tide. Measuring the distance the tide will have moved the boat along this line then gives an "estimated position" or EP (traditionally marked with a dot in a triangle). A tidal atlas is used to predict the direction and speed of tadal currents. ...
A knot is a non SI unit of speed equal to one nautical mile per hour. ...
Tidal diamonds are marks on an Admiralty Charts used to calculate direction and speed of tidal streams. ...
Dead reckoning is the process of estimating a global position of a vehicle by advancing a known position using course, speed, time and distance to be traveled. ...
All nautical charts have depth markings on them which give "chart datum" - the depth of water at that point during the lowest possible astronomical tide (tides may be lower or higher for meteorological reasons). Heights and times of low and high tide on each day are available in "tide tables". The actual depth of water at the given points at these times can then be calculated by adding the figures given to the depth given on the chart. Depths for intervening times can be calculated from tidal curves (each port has its own). If an accurate curve is not available, the rule of twelfths can be used. This approximation works on the basis that the increase in depth in the six hours between low and high tide will follow this simple rule: first hour - 1/12, second - 2/12, third - 3/12, fourth - 3/12, fifth - 2/12, sixth - 1/12. A nautical chart is a graphic representation of a maritime area and adjacent coastal regions. ...
The chart datum is the theoretical level of water in any tidal area during the lowest possible astronomical tide (LAT). ...
A tide table is used for tidal prediction and shows the daily times and height of high water and low water for a particular location. ...
(N.B. It would be foolish to attempt navigation without some training and the "Rule of Twelfths " in particular should be used with caution)
Other tides In addition to oceanic tides, there are atmospheric tides as well as terrestrial tides (land tides), affecting the rocky mass of the Earth. Atmospheric tides are negligible, drowned by the much more important effects of weather and the solar thermal tides. The Earth's crust, on the other hand, rises and falls imperceptibly in response to the Moon's solicitation. The amplitude of terrestrial tides can reach about 55 cm at the equator (15 cm of which are due to the Sun), and they are nearly in phase with the Moon (the tidal lag is about two hours only) - which means that they reinforce the apparent oceanic tides.
While negligible for most human activities, terrestrial tides need to be taken in account in the case of some particle physics experimental equipments (Stanford online). For instance, at the CERN or SLAC, the very large particle accelerators are designed while taking terrestrial tides into account for proper operation. Indeed, despite their kilometre-range dimension, centimetric deformations might lead to their malfunctioning as a physics experimental apparatus. Among the effects that need to be taken into account are : circumference deformation for circular accelerators, particle beam energy. Particles explode from the collision point of two relativistic velocity (100 GeV) gold ions in the STAR detector of the Relativistic Heavy Ion Collider. ...
CERN logo CERN is the European Organization for Nuclear Research, the worlds largest particle physics laboratory, situated on the border between France and Switzerland, just west of Geneva. ...
The Stanford Linear Accelerator Center (SLAC) is a U.S. national laboratory operated by Stanford University for the U.S. Department of Energy. ...
One of the early particle accelerators responsible for development of the atomic bomb. ...
The first mathematical explanation of tidal forces was given in 1687 by Isaac Newton in the Philosophiae Naturalis Principia Mathematica. Events March 19 - The men under explorer Robert Cavelier de La Salle murder him while searching for the mouth of the Mississippi River. ...
Sir Isaac Newton in Godfrey Knellers 1689 portrait Sir Isaac Newton (25 December 1642 – 20 March 1727 by the Julian calendar in use in England at the time; or 4 January 1643 – 31 March 1727 by the Gregorian calendar) was an English physicist, mathematician, astronomer, philosopher, and alchemist who...
Newtons own copy of his Principia, with hand written corrections for the second edition. ...
Tsunami, the large waves that occur after earthquakes, are sometimes called tidal waves, but have nothing to do with the tides. Other phenomena unrelated to tides but using the word tide are rip tide, storm tide, and hurricane tide. The term tidal wave appears to be disappearing from popular usage. Tsunami - Wikipedia, the free encyclopedia /**/ @import /skins-1. ...
Riptide redirects here. ...
A storm tide is a tide with a high flood period caused by a storm. ...
See also Coastal erosion is a process which affects the landmass of an area as a consequence of the sea acting upon it. ...
The Hough functions in applied mathematics are the eigenfunctions of Laplaces tidal equations which govern fluid motion on a rotating sphere. ...
The primitive equations are a version of the Navier-Stokes equations which describe hydrodynamical flow on the sphere under the assumptions that vertical motion is much smaller than horizontal motion (hydrostasis) and that the fluid layer depth is small compared to the radius of the sphere. ...
A storm tide is a tide with a high flood period caused by a storm. ...
The tidal bore in. ...
A tidal island is a piece of land that is connected to the mainland by a causeway exposed at low tide and submerged at high tide. ...
In oceanography, tidal resonance is a phenomenon perhaps best exemplified in the Bay of Fundy. ...
A rip current is a strong flow of water returning seaward from the shore. ...
Tide pools at a beach Closeup of a tide pool with some algae and barnacles Tide pools are areas on rocks by the ocean that are filled with seawater. ...
Slack water is the time during which no appreciable current in flowing in a body of water. ...
Tidal power is a means of electricity generation achieved by capturing the energy contained in moving water mass due to tides. ...
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