Tide

The tide or tidal ( low German Tid, Tied [ ti ː t] "time"; Tides Pl, Tieden [ ti ː dən ] "Times" ) are driven by tidally periodic movement of water of the oceans. Periods between high tide and low water are referred to as low tide periods between low and high water as a flood.

The forces acting on the earth tidal forces caused by the gravitation ( attraction) between Earth and the Moon and Earth and Sun. The earth is also compared to the moon distance and even greater distance from the Sun so large that the attractive forces of the moon and the sun is not at all places are the same and therefore there are tidal forces. Although the sun is much farther away from Earth than the moon, but it caused tidal forces as are almost half the size coming from the moon. Their cause is compared to the moon much larger mass.

The tidal forces change in different places of the earth's surface as a result of Earth's rotation on a regular basis and raise and lower the sea level periodically. The stroke caused, for example, the moon is only about 30 cm. The associated water currents lead but to the seashores to the rise and fall of the water level in the order of meters. In some places resonant vibrations with very large tidal range may result in appropriate coastal and seabed shape.

The doctrine of the maritime tides of the earth is called tidal customer and is part of the nautical training.

• 8.1 Modern tidal theory
• 8.2 Other effects of tidal forces

• 9.1 Selected Tidenhübe in the southern North Sea

General Description

Two celestial bodies would move towards one another and collide as a result of mutual attraction. A stable distance exists when they rotate against each other. In this case the attraction force is the centripetal force which is necessary for the circulation.

This means that, for example, the attraction of the moon through the Earth's orbit around the common center of gravity with the moon is compensated primarily (pictured left). In the reference frame of the Earth can be determined as a result of this cycle one of the attraction of oppositely directed centrifugal force. This acts everywhere in the same size, because all points of the earth rotate on circles of the same radius ( right). The attracting force is, however, in various points of the earth differ in size, generally on the side facing the moon is greater than on the opposite side. In the priority it is canceled by the centrifugal force, otherwise there remains a small, tidal power called Resulting directed almost everywhere outside ( "up" ). She is at two opposite points of the earth's surface is greatest, namely where it is pierced by the passing through the centers of gravity of Earth and Moon line ( often referred to himself as the maximum value of tidal power ). It is radially outwardly. Consequently, a mountain flood occurs not only on the moon -facing surface of the earth, but also against.

When viewed from outside the Earth only attraction or gravitational forces are balanced, namely the locally different forces acting in the earth gravity force. This makes it clear that the tidal power, although a consequence of gravitation, but only one of these is subordinate. The tidal power is thus substantially smaller than the gravitational force causing.

The originating from the solar tidal force is about 45 percent that of the moon. In full and new moon Sun, Earth and Moon are approximately on a straight line, then add the attraction effects, and there is a (higher) spring tide. No addition takes place when the Sun, Earth and Moon are at right angles, as in Crescent, each other. It comes here in a lower neap tide. During a lunar phase period ( about 29.5 days) vary the Tidenhübe almost regularly. Irregularities are mainly a result of the weather, in particular the changing wind conditions ( storm surge ) that can have a huge impact on the tide compared to the astrophysical influences. Regular long-term changes occur because of the north-south displacement of the sub-solar point ( in the end ), the rotation of the line of apses on the moon (period: 8.85 years ) and the line of nodes ( 18.61 years " Nodaltide " period).

Two statements

Statement when viewed from the outside

The different attraction by the moon shapes the mass particles of the earth on a different path radius, a smaller on the facing or greater on the opposite side. The Earth's body is too rigid to noticeably to stretch between to and remote from the side. But only the gravity unsuccessful waters of the seas can rise above the mean level and form on each side a small mountain flood.

Informative when viewed from the ground

The earth moves as a whole nearly circular around the common center of gravity with the moon. The appearing as a radial force in its focus on medium-sized lunar attraction can be seen on Earth as the same everywhere seriously addictive. On the side facing the moon whose attraction is larger, so that a small -pointing in his direction the mountain flood occurs. On the side facing away from the centrifugal force is greater, and there is also a flow mountain.

Frequency and size of the tides

The time for one revolution of the tidal forces around the Earth is determined by the daily (24 hours) rotation of the earth and the monthly ( 27.32 days ) orbit of the moon around the earth. Since intrinsic rotation and the Moon's orbital have the same direction, the total period is longer than a self-rotation, namely about 24 hours and 50 minutes.

For the size of the maximum tidal acceleration ag following formula applies:

For the tidal effect of the moon on the earth is ag with

This is just about the 10-7 times the acceleration due to gravity ( 9.81 m/s2), which is why the sea level is also increased by only about 30 cm by the tidal pull of the moon.

Does not apply to the approximation in the above formula contained in, results in the account that the magnitude of acceleration as the tide is at the side facing away from the moon about 5% smaller on the side facing (AG1 ≈ 0.95 AG2):

Cause is non-linear decrease of attraction.

Your outgoing value from the moon is

About 30 times greater than the tidal acceleration ag, which is why the latter is rightly called one of the downstream gravitational phenomenon.

The following control statement shows the agreement of the absolute values ​​of the gravitational acceleration at the Earth gravity and the detectable anywhere on earth (earth - fixed reference system ) centrifugal acceleration az, which in turn is calculated the same as the centripetal acceleration:

The tidal power scales with the cube of the distance from the center of gravity and falls off faster than the gravitational force, which scales quadratically. This means that the tidal forces of the moon much closer to the Earth are larger than those of the sun with 2.7 × 107 -fold mass and consequently almost 180 times the force of gravity.

The arising of the sun on the earth tide acceleration ag is

And the gravitational acceleration is

Compared to the moon the sun and some planets cause the following tidal effects on the Earth:

The tabulated deflection is the rise of the water level on the open sea.

Tides account

With tidal calculations predict the time course of the tides and the height of the tide can be made. The phases of the tides have an appreciable impact on coastal shipping. It must be adjusted when the depth of water is too low. The tidal flow can speed up or slow shipping. The time when it is changing its direction of capsizing point, one of the calculated predictions. Special effect on the shipping industry has the tidal wave traveling at high tide by a river mouth in the interior.

History of tidal theory

Already the Greek natural philosophers (among Aristotle and Seleucus of Seleucia ) developed theories to explain the tides. It was recognized as the tides depends on the Moon and its phases, you generally archaic ideas of the lunar influence, for example, the weather, notes, and the relationship between the tides and the moon was the Indians, Phoenicians and Carians known.

Published in the 14th century Jacopo Dondi ( dall'Orologio ), father of Giovanni de Dondi ( dall'Orologio ), De fluxu et refluxu maris, probably inspired by Greco- Byzantine sources, edited in 1912 by P. Revelli.

In the 16th century Andrea Cesalpino explained the tide in his work Quaestiones Peripatetica (1571 ) with the earth's movement - similar to the movement of water in a moving bucket. 1590 Simon Stevin presented on the theory that the tide could be explained by the attraction of the moon.

Galileo Galilei developed in the early 17th century a kinematic tidal theory, which he published Dialogo (1632 ), and led the Tide to as evidence of the Earth's rotation. According to his theory, the illuminated side of the Earth from the Sun is moving slower than the night side, so that the tide will result due to the different accelerations. Johannes Kepler declared 1609 the tide by gravitation of the moon. René Descartes postulated in the 17th century, a theory based on a friction of the " ether " between the earth and moon. This theory was refuted quickly.

Isaac Newton was able to show the first predictable that the attractive forces of the masses of the sun and moon for the tides are the cause. In his published work in 1687 Mathematical Principles of Natural Philosophy, he postulated a gravitational system of Earth and the Moon, rotating around a gravitational center, the common center of mass ( barycenter ).

Emergence of the tides

Moon and Earth form a system with a common center of gravity, the Earth-Moon center of gravity. Both moon and earth both revolve around this system focus, which is also called the barycenter. Since the mass of the Earth is 81 times as large as that of the moon, this focus is still in the bowels of the earth. It is 4680 km away from the Earth's center (the radius of the Earth is approximately 6371 km ).

The earth performs the movement around the system center of gravity as a rigid whole. Through this circular movement is an identical acceleration ( centrifugal and ) at each point of the earth. This centrifugal force is therefore everywhere on Earth the same size and has the same direction: parallel to the line center of the Earth - Moon center of the moon groundbreaking. Depending on the position on the ground, it is directed into the earth under the circumstances.

The gravitational field of the moon produces a nearly opposite acceleration for each of these points. Averaged over the entire earth is both accelerations cancel. Through this balance moon and earth run on stable orbits. The Moon 's gravitational field, however, does not carry on any point on earth from the same acceleration. On the lunar near side of the Earth 's gravitational field is slightly stronger than the centrifugal force facing into the earth, and forms the first flood mountain. On the lunar far side of the moon facing away from the centrifugal force is stronger than the moon's gravity, and it forms the second flood mountain.

It is not intuitively understood that the centrifugal force to be identical by the earth around the system center of gravity at any point on earth. From personal experience, everyone knows that the centrifugal force with increasing speed ( the car too fast is carried out of the curve) or decreasing radius ( close to cornering does not succeed ) increases. So we now consider all occurring forces in the moving Earth-Moon system ( estimates ):

• Earth's gravity, acceleration 9806.65 mm / s ²
• Rotation of the Earth around the center of the Earth, acceleration 33.9 mm / s ²
• Revolution of the Earth around the system center of gravity, acceleration 0.0332 mm / s ²
• Moon's gravity, acceleration 0.0321 to 0.0343 mm / s ²

Adding up all these forces, taking into account the direction in which they act ( vectorial), we obtain for any point on earth an acceleration value and thus the tidal forces. Accelerations occur whenever the state of motion of an object is changed. This means that the object has to change the speed or direction of movement. The inertia exerts any accelerated mass an acceleration of the opposing force. So if we want to investigate the centrifugal force, we need only consider all the speed and direction changes. Summing up the speed and the direction of movement to a vector together can detect both of these aspects in a computing step. The problem is thus reduced to the addition of vectors. It does not matter in which order we add, the result remains the same.

Let's start with the revolution of the Earth around the system center of gravity. This takes about as long as the orbital period of the Moon around the Earth. The earth moves itself as a whole. The Center of the Earth moves on a circular path around the system center of gravity as the center. All other points move with the center of the earth, for they are firmly attached to it. Each point therefore moves on a circular path with the same radius, but to each its own center. This center is always the same distance moved to the system focal point as the point itself from the Earth's center. Warning: The Earth and each of its points are not rotated in this analysis, not even to the center of the earth! Its orientation in space is fixed and it is so to speak slid along a circular path. Try the best with a beer mat on the table, without rotating the wrist here. The centrifugal force generated is the same at every point of the earth, for speed and radius are the same for each point. The direction of the centrifugal force is parallel in all respects. In the center of the earth it points away from the system focus. The value is around about 0.0332 mm / sec ². Far away on the opposite side of the system center of gravity is the moon and its mass generates its gravitational field. If you drop an object in a gravitational field, it accelerates in the direction of the center of gravity. For each point of a gravitational field so you can specify an acceleration vector. We choose three points on the earth's surface relatively to the moon:

• (A) The next item ( mondnah )
• (B ) the most distant point ( moon away )
• (C ) intermediate point

All three points lie on the same latitude. The intermediate point lies on the surface, in the center between crescent near and mondfernem point. On the moon near point the gravitational field produced an acceleration of about 0.0343 mm / s ². This is slightly more than the calculated centrifugal force up to now. The acceleration is, oriented to the moon, so opposite to the centrifugal force. So we simply need to subtract both values ​​. The difference of 0.0011 mm / s ² corresponds to a tiny acceleration in the direction of the moon. On the other side of the earth, the moon's gravity is only about 0.0321 mm / s ². The directions remain the same, so we subtract again and get -0.0011 mm / s ². So this time, the centrifugal force is stronger and the resultant acceleration is pointing away from the moon. At intermediate point we can not simply subtract the amounts, because centrifugal force and gravity do not show in the same direction. Therefore, the result is not zero, but the result is a tiny component of acceleration in the direction Erdinneres.

If we add now the earth's gravity of 9806.65 mm / s ². This is a very high figure, compared with the calculated until now accelerations. However, it is the same for every point on the earth's surface and shows at exactly the center of the earth. So the Earth's gravity does not contribute to explaining differences in accelerations.

If we add now the centrifugal force of the rotation of the Earth about its axis. It acts against the earth's gravity at any point as it is directed contrary to the outward. However, it is much weaker. It is, along the width extent of equal size and can not help to produce different accelerations as well.

Thus, the tidal explained solely by the difference of inhomogeneous moon's gravity field and constant centrifugal force through revolution to the system focus.

Intuition to mathematics

Why that contradicts so much of our intuition? There are also the following view: rotation and revolution of the earth have the same direction of rotation. On the lunar near side, therefore subtracting their speeds. On the lunar far side, they add up. In reality, we move to a moon near- point much more slowly through the room as on the lunar far side. The difference is about 25 meters per second. Add to that the true path is not circular around the room, but rather corresponds to an elongated spiral. Nevertheless, these values ​​arise only by adding two rotations that can be analyzed individually in any order. The results from the fact that ultimately only adds velocity vectors. A point on this orbit is subject, in fact, different strong accelerations. The results from the fact that the angle between the centrifugal forces of rotation and revolution of changes every second for each point of the earth's surface. But that does not matter, because the gravitational field of the moon adds to the centrifugal force through revolution always be zero, except for the tiny tide forming deviations. What remains is then only the relatively strong centrifugal force of the rotation around the center, which at all points along a latitude is equally strong but. This computing sequence is indeed intuitive, but also more complex, and ultimately leads but the same result as the mathematically simpler way.

The tidal forces pull the earth to a certain extent in the length and lead to the ends to each of a mountain flood, with the Earth's diameter is reduced accordingly in the area between these flood mountains. In a completely covered with ocean earth would result in a variation in height of 50 cm. The moon's gravity takes the square of the distance to the moon. This forces the difference on the lunar near side is higher than on the distant moon. Therefore, the flood peak in the lunar near side is about 7 percent higher. The appropriate flood is also known as Zenit flood.

Ebb and flow

Tide is the period and the process rising or " accruing " water. Low tide is the period and the process sinking or " running " water. Specify the time of highest water level is referred to with high water ( HW), the deepest of the water level with low water ( NW). The water level at these times is called flood height ( HWH ) or low water height ( NWH ). Successive high water and low water heights are different, as we are changing the positions of the Moon and Sun relative to the Earth. The date of the change of the flooding to water running off (or vice versa ) is called the capsize. When the tide capsizing it comes to a brief halt the tidal current. This is known as the backwaters.

The height difference between low water level and the following high water level ( during high tide ) is called Tidenstieg. The difference in height between high tide level and the following low water level ( during low tide ) will be referred to alsTidenfall. The mean of Tidenstieg and Tidenfall is called tidal range. The time course of the water level between low water, high water and subsequent low water yields the Tidenkurve. The tidal height of the water level based on the local chart datum (mostly LAT ) is called the height of the tide.

Tidal water levels:

The German abbreviations are no longer used in official works of the IHO.

Tidal differences:

Chart Datum:

Tidal theory

In 24 hours the Earth rotates once around itself and the moon passes through its apparent path in the sky every day about 50 minutes later. This results in that 12 hours, 25 minutes pass between two Tidehochwässern. So there are usually twice daily high and low tide. Due to the coastal morphology (see below), the tilt of Earth's axis and the elliptical orbit of the moon around the earth stood addition variations in the distances of successive high and low water levels. In the open ocean, such as in the Azores, this variation is approximately one hour. In estuaries, the variations are larger in Hamburg, for example, to over two hours. Due to the formation of nodes ( see below) but they may also turn out lower. So this variation is for example in Wilhelmshaven around 40 minutes.

The tidal force of the moon in the oceans is approximately 0.0000001 ( 10-7 ) of the force which the earth exerts on the water in the oceans by their gravity. The moon alone can thus raise the water level only slightly. The water loses in the areas where the tidal force acts on weight. The relative weight loss (not weight loss ) equal to the pull of the moon there about 0.0001 %. This weight loss causes in the areas of tidal power a pressure reduction in the water of the oceans, so that water flow is triggered. The water flow results in a material shift in the oceans, in the Tidenberge. The (not real) static case, ie in a non-rotating Earth, this process would be continued until the surface of the ocean has accepted an equipotential surface in the combined gravitational field of the Earth and Moon. This equipotential surface is located at the maximum of about 60 inches higher than the undisturbed surface of the oceans. Real this static condition is not achieved due to the Earth's rotation, or overlaid by the occurring current and wave processes. However, the tidal force is the excitation of the entire process.

Modern tidal theory

Alone with the gravitational theory can not fully explain the tides. Although the approach based on the gravity and the Earth's rotation is the same in many places with reality and allows there almost correct predictions. However, there are many regions where the reality is completely different. The theory that the earth under two flood mountains rotates through it, the continents stand in your way. A tidal tidal wave in the Atlantic case, for example on the east coast of America. It is reflected and thus runs counter to the next tidal wave.

Modern tidal theories are based on the approach of George Biddell Airy, which has been developed by Henri Poincaré, Joseph Proudman and Arthur Doodson. This hydrodynamic- empirical theory is that the tides caused by the fact that different tidal waves slosh around in the ocean basin between the continental land masses and are excited by the gravitational energy of the earth / sun cycles. A large tidal range occurs wherever the topography allows a resonance between these cycles and the moving water masses.

To this day, it is not possible to predict the tides for any location in the world solely from theoretical findings. Specifically, first, the seabed would be exactly measured and from this model are calculated based on historical measurements. To calculate the tide tables German North Sea ports, the " harmonic representation of inequalities " are used.

Other effects of the tidal forces

Since part of the Earth's core and mantle and liquid - crust are elastic, the tidal forces also cause deformation of the earth's surface. The tidal forces act on the entire volume of the earth. Just like in the oceans occurs in the liquid material of the Earth's interior to pressure fluctuations that occur in the total liquid volume of the Earth's interior. The tidal force is becoming weaker with increasing depth, however, the pressure difference to the regions where no tidal force increases with depth. The pressure changes occur with the period of tidal power. As in any liquid, caused by these pressure fluctuations in the Earth's interior material flows. Since this is the flow of a conducting fluid in the magnetic field of the earth, the effects of the MHD ( MHD) can be expected. This also applies to the waters of the oceans, where the currents of the tides are obvious. Fluctuations in the magnetic field of the earth depends on the moon and the sun, and can be partly explained by this magneto- hydrodynamic effect.

The deformation of the surface is effected with a delay of about two hours, but still with a vertical movement of 20 to 30 ( even in the equatorial region 50) centimeters.

The seas can follow tidally easier, especially their horizontal components occurring before and after the flood mountains. Tides represent in part the difference between the movements of the oceans and the earth's crust is, and the other part a consequence of the complex ( depending on geography ) flow and wave processes in the oceans, which are excited by the tidal force.

The deformation of the earth by tidal forces affects the entire volume of the Earth, and not, as is often assumed, only the oceans. The tide rain in the earth continuously a standing seismic wave, which can be measured with seismographs, provided that these long-period for the measurement signals are interpreted. This is discussed, among others, in the Erdspektroskopie. The phenomenon is particularly impressive visible on the coasts of the oceans, in part because it is there very much reinforced by currents.

The deformation of the earth by the tidal force is much smaller than the Earth flattening of 21 km as a result of Earth's rotation, but does not really stand because it is static and the sluggish earth's crust has had sufficient time to adapt to the huge change in the equipotential surface.

Coastal phenomena

Near the coast, the tides are substantially affected by the geometric shape of the coastline. This applies to both the tidal range, as well as the date of occurrence of the tides. Thus, the tidal range along the coasts of the world's oceans is often greater than in the open sea. This is especially true for funnel-shaped coastlines. The sea sloshing at high tide, so to speak to the coast. Thus, the tidal range in the western Baltic Sea is only about 30 centimeters at the German North Sea coast about one to two meters. In the North Sea tides sloshing in a circular shaft through their entire basin. In estuaries ( mouths ) of the tidal rivers, such as the Elbe and Weser, is the tidal range due to the funnel effect in these sections mentioned also Tidefluss to over four meters. Even higher is the tidal range, for example at St. Malo in France or in the Severn estuary between Wales and England. He can be reached there about eight meters. In the Bay of Fundy, the world's highest tides occur at 14 to 21 meters.

The increase in the height of the tsunami on the coasts takes place in about the same principle as in a tsunami. The speed of the tidal wave is reduced in shallow water, where the height of the wave increases. In contrast to the tsunami, tidal wave, however, is not the result of a single pulse, but contains a component which is always excited by the new tidal power.

The excited by the tide at sea on the coasts of the sea oscillations can also lead to vibration nodes at which no tidal range occurs ( Amphidromie ). Tides rotate around a certain extent such nodes. There is on the one hand low tide, so there is on the opposite side flood. This phenomenon can be found especially in marginal seas such as the North Sea, the node has two such ( see the corresponding figure in the article Amphidromie ). Outstanding here is mainly the Tideresonanz the Bay of Fundy.

Due to the tidal considerable amounts of energy to be implemented especially near the coast. In this case, the kinetic energy of the flows or the potential energy can be used by means of a tidal power plant.

Selected Tidenhübe in the southern North Sea

The Thames estuary with its very high tidal range is a classic example that at very high tides and erosion, sedimentation is so strong so low that it forms an estuary. In the Rhine - Meuse -Scheldt delta sedimentation and erosion have worked together for thousands of years. The Sedmentation has meant that the leading- silted rivers broke out and new beds, whereby a plurality of estuaries originated. Between Antwerp and Rotterdam, where the tidal range is large, the tidal currents pendulum these estuaries have expanded to estuaries. On the flat coastline to the east of the Dutch dune belt storm surges are from the early 12th to the early 16th century, far penetrated into the country, and have washed out of the mouth of the easternmost Rheinarms IJssel from the Zuiderzee, at the mouth of the Ems the Dollard and further east the Jade Bay. Between this and the estuary of the Weser, from the beginning of the 14th to the early 16th century, a Weser Delta from estuaries and flood channels, which was similar to the Delta in Zeeland.

The tidal range differs not only between different regions; on offshore islands and Kapp it is less than on the mainland coast, in bays and estuaries sometimes higher than at the front coast. With the dredging of shipping lanes for maritime traffic, the high tidal range of the estuary ranges today in the estuaries far upstream, where he. Earlier significantly subsided (See deepening of the Elbe and Weser correction ) Upstream, the intertidal is nowadays in many places limited by weirs, which guarantee at the same time as dams in the rivers feeding a minimum water level.

Repercussions on Earth and the Moon (tidal friction)

The Tide also acts back on the main polluter, the moon back. Since the flood peaks of the connecting line between Earth and the Moon's center are slightly shifted with respect to the direction of this rotation motion due to Earth's rotation and inertia, the attraction of the masses involved when the moon is not directed exactly to the moon to the Earth's center back ( As the Earth rotates faster the earth orbits, and because of the inertia of the currents, the tide mountains always run "before the moon "). Due to the larger mass of the zenith flood and its shorter distance to the moon this results in a force on the moon, which has a small component in the direction of flight, so the moon permanently energy and angular momentum are supplied. The loss of rotational energy of the earth is not limited to the transfer of energy to the moon. Occur in addition frictional losses due to the currents on and in the earth and magneto- hydrodynamic losses (see magnetohydrodynamics, MHD). The above mentioned tidal power plants would contribute to this loss of energy.

In a more detailed analysis of energy and angular momentum in this process must be accounted for separately because each is a law of conservation of both quantities in physics. The following explanations go for better intelligibility from an isolated Earth-Moon system. This is not a complete model, as there are planets and the sun, which interfere with this system (lane disorder) and in turn exert tidal forces.

Energy Conservation: The earth is losing rotational energy by the deceleration due to the tides. This energy is found in the rotational energy of the moon, a heating (heat energy) of the earth by friction, the currents in the Earth's interior (kinetic energy) and the triggered by an MHD process changes in the magnetic field of the earth again (more precisely, electromagnetic field ).

Conservation of angular momentum: The angular momentum loss during the deceleration of the Earth's rotation is transferred to the angular momentum of the moon in its orbit around the Earth, the angular momentum of flows within the Earth, and the Earth's magnetic field of the earth.

The deceleration of the earth, and the transfer of angular momentum and rotational energy to the moon, the distance between the earth and the moon is increased by about 4 cm per year. The drag on the flood mountains leads to a torque which slows the Earth's rotation. Thus, the days lengthen each year by about 16 microseconds. 500 million years ago lasted a day on earth only about 21 hours.

These representations illustrate the physical processes in the Earth's rotation deceleration ( The same considerations apply vice versa for the influence of the tidal force of the earth on the moon. ).

The tides have on the mechanism described above influence on the Earth's rotation. It is important that the angular momentum is a vector having a magnitude and a direction. The transfer of angular momentum of the Earth on orbital angular momentum of the moon also causes a change of rotational axes. The International Earth Rotation and Reference Systems Service ( IERS ), which recommends, among other things, the setting of leap seconds, is the international coordinating institution in matters of Earth's rotation. So far, the days duration was extended in each case only to leap seconds, never shortened. The tides have an interest in the cause.

Were actually measured continuous oscillations ( standing wave ) as seismic waves of the earth, which are excited by the tide (see Erdspektroskopie ).

Tidal effect in other heavenly bodies

The comet Shoemaker- Levy 9 was approaching the Jupiter by its tidal effect torn into several parts, insist on traveling separately.

The tidal effect of Jupiter also prevents bunching of the asteroid belt a planet. For example, if two asteroids Jupiter happen, it pulls him closer to the stronger than the more distant. The distance between the asteroids increases.