What determines the ebb and flow of water. Highest tides

October 15th, 2012

British photographer Michael Marten has created a series of original shots that capture the coast of Britain from the same angles, but different time... One shot at high tide and the other at low tide.

It turned out very unusual, but positive reviews about the project, literally forced the author to start publishing the book. The book, titled "Sea Change", was released in August this year and was released in two languages. It took Michael Marten about eight years to create his impressive series of images. The time between high and low water is on average a little more than six hours. Therefore, Michael has to linger at each location longer than just a few clicks of the shutter. The idea of ​​creating a series of such works was hatched by the author for a long time. He was looking for how to implement changes in nature on film, without human influence. And I found it by chance, in one of the seaside Scottish villages, where I spent the whole day and found the time of ebb and flow.

Periodic fluctuations in water level (rises and falls) in water areas on Earth are called ebbs and flows.

The highest water level observed in a day or half a day during high tide is called full water, the lowest level at low tide is called low water, and the moment these limit levels are reached is the standing (or stage), respectively, of high tide or low tide. Average sea level is a conventional value, above which the level marks are located during high tides, and below - during low tides. This is the result of averaging large series of urgent observations.

Vertical fluctuations in the water level during high and low tides are associated with horizontal movements of water masses in relation to the coast. These processes are complicated by wind surge, river runoff and other factors. Horizontal movements of water masses in the coastal zone are called tidal (or tidal) currents, while vertical fluctuations in the water level are called ebb and flow. All phenomena associated with ebb and flow are characterized by periodicity. Tidal currents periodically change direction to the opposite, in contrast to them oceanic currents, moving continuously and unidirectionally, are caused by the general circulation of the atmosphere and cover large areas of the open ocean.

The ebb and flow of the tide cyclically alternate in accordance with the changing astronomical, hydrological and meteorological conditions. The sequence of the ebb and flow phases is determined by two highs and two lows in the diurnal cycle.

Although the Sun plays a significant role in tidal processes, the decisive factor in their development is the force of the Moon's gravitational attraction. The degree of influence of tidal forces on each particle of water, regardless of its location on the earth's surface, is determined by the law universal gravitation Newton.

This law states that two material particles are attracted to each other with a force directly proportional to the product of the masses of both particles and inversely proportional to the square of the distance between them. It is understood that the more the mass of the bodies, the greater the force of mutual attraction arising between them (at the same density, a smaller body will create less attraction than a larger one).

The law also means that the greater the distance between two bodies, the less the attraction between them. Since this force is inversely proportional to the square of the distance between two bodies, the distance factor plays a much greater role in determining the magnitude of the tidal force than the masses of bodies.

The gravitational attraction of the Earth, acting on the Moon and keeping it in near-Earth orbit, is opposite to the Earth's gravity by the Moon, which seeks to displace the Earth towards the Moon and "lifts" all objects on Earth in the direction of the Moon.

The point on the earth's surface located directly under the Moon is only 6400 km away from the center of the Earth and, on average, 386 063 km from the center of the Moon. In addition, the mass of the Earth is 81.3 times that of the Moon. Thus, at this point on the earth's surface, the Earth's gravity acting on any object is approximately 300 thousand times greater than the Moon's.

It is widely believed that water on Earth, located directly under the Moon, rises in the direction of the Moon, which leads to an outflow of water from other places on the earth's surface, however, since the attraction of the Moon is so small compared to that of the Earth, it would not be enough to raise such huge weight.
Nevertheless, the oceans, seas and large lakes on Earth, being large liquid bodies, are free to move under the force of lateral displacement, and any slight tendency to shear horizontally sets them in motion. All waters that are not directly under the Moon are subject to the action of the component of the force of attraction of the Moon, directed tangentially (tangentially) to the earth's surface, as well as its component directed outward, and are subject to horizontal displacement relative to the solid earth's crust.

As a result, there is a flow of water from the adjacent areas of the earth's surface towards a place under the moon. The resulting accumulation of water at a point under the Moon creates a tide there. The actual tidal wave in open ocean has a height of only 30-60 cm, but it increases significantly when approaching the shores of continents or islands.
Due to the movement of water from neighboring regions towards a point under the Moon, corresponding ebb tides of water occur at two other points located at a distance equal to a quarter of the Earth's circumference. It is interesting to note that a drop in sea level at these two points is accompanied by a rise in sea level not only on the side of the Earth facing the Moon, but also on the opposite side.

This fact is also explained by Newton's law. Two or more objects located on different distances from the same source of gravity and, therefore, subject to acceleration of gravity of different magnitude, move relative to each other, since the object closest to the center of gravity is most strongly attracted to it.

Water at the sublunary point experiences a stronger attraction to the Moon than the Earth below it, but the Earth, in turn, is more attracted to the Moon than water on the opposite side of the planet. Thus, a tidal wave arises, which is called forward on the side of the Earth facing the Moon, and backward on the opposite side. The first of them is only 5% higher than the second.

Due to the rotation of the Moon in its orbit around the Earth, between two successive high tides or two low tides, approximately 12 hours and 25 minutes pass at a given location. The interval between the culminations of successive ebb and flow is approx. 6 hours 12 minutes The period of 24 hours 50 minutes between two successive tides is called tidal (or lunar) days.

Inequalities in the magnitude of the tide... Tidal processes are very complex, so there are many factors that need to be taken into account to understand them. In any case, the main features will be determined:
1) the stage of development of the tide relative to the passage of the moon;
2) the amplitude of the tide and
3) the type of tidal fluctuations, or the shape of the curve of the course of the water level.
Numerous variations in the direction and magnitude of the tidal forces create a difference in the magnitude of the morning and evening tides in a given port, as well as between the same tides in different ports. These differences are called tide inequalities.

Semi-daily effect... Usually, during the day, due to the main tidal force - the rotation of the Earth around its axis - two complete tidal cycles are formed.

If you look from the North Pole of the ecliptic, then it is obvious that the Moon revolves around the Earth in the same direction in which the Earth revolves around its axis - counterclockwise. With each subsequent revolution, this point on the earth's surface again takes a position directly under the Moon a little later than during the previous revolution. For this reason, the ebb and flow of the ebb and flow every day are delayed by about 50 minutes. This value is called lunar lag.

Half-month inequality... This main type of variation is characterized by a periodicity of about 143/4 days, which is associated with the rotation of the Moon around the Earth and its passage through successive phases, in particular syzygies (new moons and full moons), i.e. moments when the Sun, Earth and Moon are located on one straight line.

So far, we have only dealt with the tidal effect of the moon. The sun's gravitational field also acts on tides, however, although the mass of the sun is much greater than the mass of the moon, the distance from the earth to the sun is so much greater than the distance to the moon that the tidal force of the sun is less than half the tidal force of the moon.

However, when the Sun and the Moon are on the same straight line, both on the same side of the Earth, and on different sides (in the new moon or full moon), the forces of their attraction add up, acting along one axis, and the solar tide is superimposed on the lunar tide.

Likewise, the attraction of the sun intensifies the ebb tide caused by the influence of the moon. As a result, the tides become higher and the ebb tides lower than if they were caused only by the gravity of the moon. Such tides are called syzygy.

When the gravitational vectors of the Sun and the Moon are mutually perpendicular (during quadratures, i.e. when the Moon is in the first or last quarter), their tidal forces oppose, since the tide caused by the attraction of the Sun is superimposed on the ebb caused by the Moon.

In such conditions, the tides are not so high, and the ebb tides are not as low as if they were due only to the force of the moon's gravity. Such intermediate ebb and flow are called quadrature.

The range of high and low water markings in this case is reduced by approximately three times compared to the syzygy tide.

Lunar parallax inequality... The period of fluctuations in the heights of the tides, arising from the lunar parallax, is 271/2 days. The reason for this inequality is the change in the distance of the Moon from the Earth during the rotation of the latter. Due to the elliptical shape of the lunar orbit, the tidal force of the moon at perigee is 40% higher than at apogee.

Daily inequality... The period of this inequality is 24 hours 50 minutes. The reasons for its occurrence are the rotation of the Earth around its axis and the change in the declination of the Moon. When the moon is near celestial equator, two high tides on a given day (as well as two low tides) differ slightly, and the heights of the morning and evening full and low waters are very close. However, as the Moon's northerly or southerly declination increases, morning and evening tides of the same type differ in height, and when the Moon reaches its highest northerly or southerly declination, this difference is greatest.

There are also known tropical tides, so called because the moon is almost over the Northern or Southern tropics.

The daily inequality does not significantly affect the heights of two successive low tides in Atlantic Ocean, and even its effect on tide heights is small compared to the overall amplitude of fluctuations. However, in the Pacific Ocean, the diurnal unevenness is manifested in the ebb levels three times more than in the tide levels.

Semi-Annual Inequality... It is caused by the revolution of the Earth around the Sun and a corresponding change in the declination of the Sun. Twice a year for several days during the equinoxes, the Sun is near the celestial equator, i.e. its declination is close to 0. The moon is also located near the celestial equator for about a day every half a month. Thus, during the equinoxes, there are periods when the declination of both the Sun and the Moon is approximately 0. The total tidal effect of the attraction of these two bodies at such moments is most noticeably manifested in regions located near the Earth's equator. If at the same time the Moon is in the phase of a new moon or a full moon, the so-called. equinox syzygy tides.

Solar parallax inequality... The period for this inequality is one year. It is caused by the change in the distance from the Earth to the Sun during the Earth's orbital motion. Once for each revolution around the Earth, the Moon is at the shortest distance from it at perigee. Once a year, around January 2, the Earth, moving in its orbit, also reaches the point of closest approach to the Sun (perihelion). When these two points of closest approach coincide, producing the greatest cumulative tidal force, higher tide levels and lower ebb tide levels can be expected. Likewise, if the passage of the aphelion coincides with the apogee, less high tides and shallower ebb tides occur.

The largest amplitudes of tides... The world's highest tide occurs with strong currents in Minas Bay in the Bay of Fundy. The tidal fluctuations here are characterized by a normal course with a semidiurnal period. The water level during high tide often rises by more than 12 m in six hours, and then decreases by the same amount over the next six hours. When the effect of syzygy tide, the position of the moon at perigee and the maximum declination of the moon fall on one day, the tide level can reach 15 m. the top of the gulf. The causes of tides, which have been the subject of constant study for many centuries, are among the problems that have generated many conflicting theories, even in relatively recent times.

Charles Darwin wrote in 1911: “There is no need to search antique literature for the sake of grotesque theories of tides ”. However, sailors manage to measure their height and use the possibilities of tides without knowing the real reasons for their occurrence.

I think that we also need not bother especially about the causes of the origin of tides. Based on long-term observations, special tables are calculated for any point in the water area of ​​the earth, which indicate the time of high and low water for each day. I am planning my trip to, for example, Egypt, which is just famous for its shallow lagoons, but try to guess in advance so that full water falls in the first half of the day, which will allow most daylight hours to fully ride.
Another tide-related issue of interest to the kiter is the relationship between wind and water level fluctuations.

A popular omen claims that the wind increases at high tide and, on the contrary, sours at low tide.
The effect of wind on tidal phenomena is clearer. The wind from the sea drives the water towards the coast, the tide height increases above normal, and at low tide the water level also exceeds the average. On the contrary, when the wind blows from the land, the water is driven away from the coast, and the sea level drops.

The second mechanism acts by increasing atmospheric pressure over a wide area, the water level drops as the superimposed weight of the atmosphere is added. When atmospheric pressure rises by 25 mm Hg. Art., the water level drops by about 33 cm. Zone high pressure or anticyclone is usually called good weather, but not for a kiter. Calm in the center of the anticyclone. A decrease in atmospheric pressure causes a corresponding increase in the water level. Consequently, a sharp drop in atmospheric pressure, combined with hurricane force winds, can cause a noticeable rise in the water level. Such waves, although called tidal waves, are not actually associated with the influence of tidal forces and do not have the periodicity characteristic of tidal phenomena.

But it is quite possible that low tides can also affect the wind, for example, a decrease in the water level in coastal lagoons, leads to a greater heating of the water, and as a consequence to a decrease in the temperature difference between the cold sea and the heated land, which weakens the breeze effect.

Photo by Michael Marten

Our planet is constantly in the gravitational field, which is created by the Moon and the Sun. This is the cause of a unique phenomenon, expressed in the ebb and flow of the earth. Let's try to figure out whether these processes affect the environment and human life.

Ebb and flow are changes in the water level of sea elements and the World Ocean. They arise as a result of vertical oscillations, depending on the location of the sun and moon. This factor interacts with the rotation of our planet, which leads to similar phenomena.

The mechanism of the phenomenon "ebb and flow"

The nature of the formation of ebb and flow has already been sufficiently studied. Over the years, scientists have investigated the causes and results of this phenomenon.

• Similar fluctuations in the water level can be shown in the following system
• The water level gradually rises, reaching its highest point... This phenomenon is called full water.
• After a certain period of time, the water begins to subside. Scientists have defined this process as "ebb".
• For about six hours, the water continues to drain to its minimum point. This change was named in the form of the term "low water".

Thus, the whole process takes about 12.5 hours. A similar natural phenomenon occurs twice a day, so it can be called cyclical. The vertical interval between the points of alternating waves of complete and small formation is called the amplitude of the tide.

You can see some pattern if you observe the tide process in the same place for a month. The results of the analysis are interesting: daily low and high water changes its location. With such a natural factor as education new moon and full moon, the levels of the studied objects move away from each other.

Consequently, this makes the tide amplitude at its maximum twice a month. The appearance of the smallest amplitude also occurs periodically, when, after the characteristic influence of the Moon, the levels of small and full waters gradually approach each other.

The causes of ebb and flow on Earth

There are two factors that influence the formation of ebb and flow. It is necessary to carefully consider both objects that affect the change in the water space of the Earth.

Impact of lunar energy on ebb and flow

Although the influence of the Sun on the cause of the ebb and flow is undeniable, the effect of lunar activity is of the greatest importance in this matter. In order to feel the significant effect of the satellite's gravity on our planet, it is necessary to trace the difference in the attraction of the Moon in different areas Earth.

The experimental results will show that the difference in their parameters is rather small. The thing is that the point on the earth's surface closest to the Moon is literally 6% more exposed to external influence than the most distant one. It is safe to say that this separation of forces pushes the Earth apart in the direction of the Moon-Earth trajectory.

Taking into account that our planet constantly turns around its axis during the day, the passage of a double tidal wave along the perimeter of the resulting tension. This is accompanied by the creation of the so-called double "valleys", the height of which, in principle, does not exceed 2 meters in the oceans.

On the territory of the earth's land, such fluctuations reach a maximum of 40-43 centimeters, which in most cases remains unnoticed by the inhabitants of our planet.

All this leads to the fact that we do not feel the force of the ebb and flow either on land or in the water element. You can observe a similar phenomenon on a narrow strip of the coastline, because the waters of the ocean or sea, by inertia, sometimes gain impressive height.

From all that has been said, we can conclude that the ebb and flow are most associated with the Moon. This makes research in this area the most interesting and relevant.

Influence of solar activity on ebb and flow

The significant remoteness of the main star of the solar system from our planet affects the fact that its gravitational effect is less noticeable. As a source of energy, the Sun is certainly much more massive than the Moon, but still makes itself felt by the impressive distance between two celestial objects. The amplitude of solar tides is almost half that of the tidal processes of the Earth's satellite.

It is a well-known fact that during the full moon and the growth of the moon, all three celestial bodies - the Earth, the Moon and the Sun - are located on one straight line. This leads to the folding of the lunar and solar tides.

During the period of direction from our planet to its satellite and the main star of the Solar System, which differs from each other by 90 degrees, there is some influence of the Sun on the process under study. There is an increase in the level of low tide and a decrease in the level of high tide of the earth's waters.

All indications are that solar activity also affects the energy of the ebb and flow on the surface of our planet.

The main types of ebb and flow

You can classify a similar concept according to the duration of the ebb and flow cycle. The disengagement will be fixed using the following items:

1. Semi-daily changes in the surface of the water space... Such transformations consist in two full and the same amount of incomplete waters. The parameters of the alternating amplitudes are practically equal to each other and look like a sinusoidal curve. Most of all, they are localized in the waters of the Barents Sea, on an extensive line of the coastal strip Of the White Sea and on the territory of almost the entire Atlantic Ocean.
2. Daily fluctuations in water level... Their process consists in one full and incomplete water for a period calculated within a day. A similar phenomenon is observed in the Pacific Ocean region, and its formation is extremely rare. During the period of the passage of the Earth's satellite through the equatorial zone, the effect of standing water is possible. If the Moon tilts with the smallest index, small tides of an equatorial nature occur. At the highest numbers, the process of formation of tropical tides occurs, accompanied by the greatest power of water inflow.
3. Mixed tides... This concept includes the presence of semi-diurnal and diurnal tides of irregular configuration. The semi-diurnal changes in the level of the earth's water envelope, which have an irregular configuration, are similar in many ways to semi-diurnal tides. In altered diurnal tides, a tendency towards diurnal fluctuations can be observed, depending on the degree of declination of the moon. The most prone to mixed tides are the waters of the Pacific Ocean.
4. Abnormal hot flashes. These rises and falls of water do not fit the description of some of the signs listed above. This anomaly is associated with the concept of "shallow water", which changes the cycle of rise and fall of the water level. The influence of this process is especially pronounced in river estuaries, where the tides are shorter in time than the ebb tides. You can observe a similar cataclysm in some parts of the English Channel and in the currents of the White Sea.

There are also types of ebb and flow that do not fall under these characteristics, but they are extremely rare. Research in this area continues, because many questions arise that require specialists to decipher.

Earth's ebb and flow chart

There is a so-called ebb and flow table. It is necessary for people who depend on the nature of their activities on changes in the earth's water level. To have exact information on this phenomenon, you need to pay attention to:

• Designation of an area where it is important to know the data on the ebb and flow of the tide. It is worth remembering that even closely spaced objects will have different characteristics of the phenomenon of interest.
• Finding the necessary information using Internet resources. For more accurate information, you can visit the port of the region under study.
• Specifying the time needed for accurate data. This aspect depends on whether the information is needed for a specific day or the study schedule is more flexible.
• Working with the table in the mode of emerging needs. It will display all the tide information.

A beginner who needs to decipher such a phenomenon will greatly benefit from the ebb and flow chart. To work with such a table, the following recommendations will help:

1. The columns at the top of the table indicate the days and dates of the alleged event. This item will allow you to find out the point of determining the time frame of the studied.
2. Under the line of temporary accounting there are numbers placed in two rows. In the format of the day, the decoding of the phases of the rising of the moon and the sun is placed here.
3. Below is a waveform chart. These indicators record the peaks (tides) and troughs (ebbs) of the waters of the study area.
4. After calculating the amplitude of the waves, the data of the arrival of celestial bodies are located, which affect the changes in the water shell of the Earth. This aspect will allow observing the activity of the Moon and the Sun.
5. On both sides of the table, you can see numbers with plus and minus indicators. This analysis is important for determining the level of rise or fall of water, measured in meters.

All these indicators cannot guarantee one hundred percent information, because nature itself dictates to us the parameters by which its structural changes occur.

The impact of ebb and flow on the environment and humans

There are many factors of the influence of ebb and flow on human life and the environment. Among them there are phenomenal discoveries that require careful study.

Killer waves: hypotheses and consequences of the phenomenon

This phenomenon causes a lot of controversy among people who trust only unconditional facts. The fact is that wandering waves do not fit into any system of the occurrence of this phenomenon.

The study of this object became possible using radar satellites. These designs made it possible to record a dozen ultra-large amplitude waves over a period of a couple of weeks. The size of such a rise of the water block is about 25 meters, which indicates the grandeur of the phenomenon under study.

Killer waves directly affect human life, because over the past decades, such anomalies have carried huge vessels such as supertankers and container ships into the ocean depths. The nature of the formation of this stunning paradox is unknown: giant waves form instantly and just as quickly disappear.

There are many hypotheses regarding the reason for the formation of such a whim of nature, but the appearance of eddies (single waves due to the collision of two solitons) is possible with the interference of the activity of the Sun and the Moon. This issue is still becoming a reason for discussions among scientists specializing in this topic.

The effect of ebb and flow on organisms that inhabit the Earth

The ebb and flow of the ocean and sea especially affects marine life. This phenomenon exerts the greatest pressure on the inhabitants of coastal waters. Due to this change in the level of the earth's water, sedentary organisms develop.

These include molluscs, which have perfectly adapted to the vibrations of the Earth's liquid shell. Oysters at the highest tides begin to multiply actively, which indicates that they respond favorably to such changes in the structure of the water element.

But not all organisms respond so favorably to external changes... Many species of living things suffer from periodic fluctuations in water levels.

Although nature takes its toll and coordinates changes in the overall balance of the planet, biological substances adapt to the conditions presented to them by the activity of the Moon and the Sun.

The impact of ebb and flow on human life

On general state human this phenomenon affects more than the phases of the moon, to which the human body may be immune. However, the most ebbs and flows affect the production activities of the inhabitants of our planet. It is unrealistic to influence the structure and energy of the ebb and flow of the sea, as well as the oceanic sphere, because their nature depends on the gravity of the Sun and the Moon.

Basically, this cyclical phenomenon only brings destruction and trouble. Modern technologies allow this negative factor to be directed in a positive direction.

An example of such innovative solutions are pools that trap such fluctuations in water balance. They must be built in a way that the project is cost-effective and practical.

To do this, it is necessary to create such pools of a rather significant size and volume. Power plants to contain the effect of tidal force water resources Lands are a new business, but quite promising.

The study of the concept of ebb and flow on Earth, their influence on the life cycle of the planet, the mystery of the origin of killer waves - all this remains the main questions for scientists specializing in this field. The solution to these aspects is also interesting for ordinary people who are interested in the problems of the influence of foreign factors on the planet Earth.

The influence of the moon on earthly world exists, but it is not pronounced. It is almost impossible to see it. The only phenomenon that visually demonstrates the effect of the attraction of the moon is the influence of the moon on the ebb and flow. Our ancient ancestors associated them with the Moon. And they were absolutely right.

How the moon affects the ebb and flow

The ebb and flow in some places is so strong that the water recedes from the coast for hundreds of meters, exposing the bottom, where the peoples living on the coast collected seafood. But with inexorable precision, the water receding from the shore rolls over again. If you do not know how often the ebb and flow occurs, you can end up far from the coast and even die under the advancing water mass. The coastal peoples knew perfectly well the timetable for the arrival and departure of waters.

This phenomenon occurs twice a day. Moreover, ebb and flow exist not only in the seas and oceans. All water sources are influenced by the moon. But far from the seas it is almost imperceptible: the water rises a little, then sinks a little.

The influence of the moon on liquids

Liquid is the only natural element that moves behind the Moon, making vibrations. A stone or house cannot be attracted to the moon because it has a solid structure. Pliable and plastic water clearly demonstrates the effect of the lunar mass.

What happens during high tide or low tide? How does the moon raise water? The Moon most strongly affects the waters of the seas and oceans from the side of the Earth, which is currently facing directly to it.

If you look at the Earth at this moment, you can see how the Moon pulls the waters of the world's oceans to itself, lifts them up, and the water column swells, forming a "hump", or rather, two "humps" appear - high on the side where the Moon is located , and less pronounced on the opposite side.

The humps closely follow the movement of the moon around the earth. Since the world's ocean is a single whole and the waters in it are connected, the humps move from the coast, then to the coast. Since the moon passes twice through points located at a distance of 180 degrees from each other, then we observe two high tides and two low tides.

Ebb and flow according to the phases of the moon

• The greatest ebbs and flows occur on the ocean shores. In our country - on the shores of the Arctic and Pacific oceans.
• Less significant ebb and flow are characteristic of inland seas.
• This phenomenon is even weaker observed in lakes or rivers.
• But even on the shores of the oceans, the tides are more powerful at one time of the year, and weaker at another. This is already due to the remoteness of the Moon from the Earth.
• The closer the moon is to the surface of our planet, the stronger the ebb and flow will be. The further - the weaker, naturally.

The water masses are influenced not only by the Moon, but also by the Sun. Only the distance from the Earth to the Sun is much greater, so we do not notice its gravitational activity. But it has long been known that sometimes the ebb and flow becomes very strong. This happens whenever there is a new moon or a full moon.

This is where the power of the Sun comes into play. At this moment, all three planets - the Moon, the Earth and the Sun - line up in a straight line. Two forces of attraction are already acting on the Earth - both the Moon and the Sun.

Naturally, the height of the rise and fall of the waters increases. The strongest will be the joint influence of the Moon and the Sun, when both planets are on the same side of the Earth, that is, when the Moon is between the Earth and the Sun. AND stronger water will rise from the side of the Earth facing the Moon.

it amazing property The moon is used by people for free energy. Tidal hydroelectric power plants are now being built on the shores of the seas and oceans, which generate electricity thanks to the "work" of the moon. Tidal hydroelectric power plants are considered the most environmentally friendly. They act according to natural rhythms and do not pollute the environment.

The oceans live by their own rules, which are harmoniously combined with the laws of the universe. For a long time, people noticed that they were actively moving, but they could not understand in any way what these fluctuations in sea level were connected with. Let's find out what is high tide, low tide?

Ebb and flow: mysteries of the ocean

The sailors knew very well that the ebb and flow is a daily occurrence. But the nature of these changes could not be understood either by ordinary residents or by scientists. As early as the fifth century BC, philosophers tried to describe and characterize how the oceans moved. seemed to be something fantastic and extraordinary. Even respected scientists considered the tides to be the breath of the planet. This version has existed for several millennia. It was only at the end of the seventeenth century that the meaning of the word "tide" was associated with the movement of the moon. But it was not possible to explain this process from a scientific point of view. Hundreds of years later, scientists figured out this riddle and gave precise definition daily changes in water level. The science of oceanology, which appeared in the twentieth century, established that the tide is the rise and fall of the water level of the World Ocean in connection with the gravitational influence of the Moon.

Are the tides the same everywhere?

The influence of the moon on the earth's crust is not the same, so it cannot be said that the tides around the world are identical. In some parts of the world, daily sea level drops reach sixteen meters. And the inhabitants of the Black Sea coast practically do not notice the ebb and flow, since they are the smallest in the world.

Usually the change occurs twice a day - in the morning and in the evening. But in the South China Sea, the tide is the movement of water masses, which occurs only once every twenty-four hours. Most of all, sea level changes are noticeable in straits or other narrow places. If you observe, then with the naked eye it will be noticeable how quickly the water leaves or comes. Sometimes it rises five meters in a few minutes.

As we have already found out, the change in sea level is caused by the impact on the earth's crust of its permanent satellite, the Moon. But how does this process take place? To understand what a tide is, it is necessary to understand in detail the interaction of all the planets in the solar system.

The moon and the earth are in constant dependence on each other. The Earth attracts its satellite, and that, in turn, seeks to attract our planet. This endless rivalry allows you to maintain the required distance between two space bodies. The moon and the earth move in their orbits, then moving away, then approaching each other.

At that moment, when the moon comes closer to our planet, the earth's crust bends towards it. This causes the excitement of the water on the surface of the earth's crust, as if it seeks to rise higher. The distance of the earth's satellite causes a decline in the level of the World Ocean.

The interval of ebb and flow on Earth

Since the tide is a regular occurrence, it must have its own definite interval of movement. Oceanologists were able to calculate exact time lunar days... This term is usually called the revolution of the Moon around our planet, it is slightly longer than the usual twenty-four hours for us. Every day the ebb and flow of the tide is shifted by fifty minutes. This time interval is necessary for the wave to "catch up" with the Moon, which moves thirteen degrees over the earth's day.

Impact of ocean tides on rivers

We have already figured out what a tide is, but few people know about the influence of these oceanic fluctuations on our planet. Surprisingly, even rivers are affected by ocean tides, and sometimes the result of this intervention is incredibly frightening.

During heavy tides, a wave entering the mouth of a river meets a stream fresh water... As a result of mixing water masses of different densities, a powerful shaft is formed, which begins to move at a tremendous speed against the flow of the river. This stream is called boron, and it is capable of destroying almost all living things on its way. A similar phenomenon washes away coastal settlements and the coastline in a matter of minutes. Bohr stops as suddenly as it started.

Scientists have recorded cases when a powerful pine forest turned rivers back or completely stopped them. It is not hard to imagine how disastrous these phenomenal tidal events have become for all the inhabitants of the river.

How do tides affect marine life?

Not surprisingly, tides have a huge impact on all organisms that live in the depths of the ocean. The hardest part is for small animals living in coastal zones... They are forced to constantly adapt to changing water levels. For many of them, tides are a way to change their habitat. During high tides, small crustaceans move closer to the coast and find food for themselves, the tidal wave pulls them deeper into the ocean.

Oceanologists have proven that many Marine life closely related to tidal waves. For example, in some species of whales, their metabolism slows down during low tides. In other deep-sea inhabitants, reproductive activity depends on the wave height and its amplitude.

Most scientists believe that the disappearance of such phenomena as fluctuations in the level of the World Ocean will lead to the extinction of many living things. Indeed, in this case, they will lose their power source and will not be able to adjust their biological clock to a certain rhythm.

The Earth's Rotation Speed: Is the Influence of the Tides Great?

For many decades, scientists have been studying everything related to the term "tide". This is a process that brings more and more riddles every year. Many experts associate the speed of the Earth's rotation with the action of tidal waves. According to this theory, under the influence of tides are formed On their way, they constantly overcome the resistance of the earth's crust. As a result, almost imperceptibly for humans, the planet's rotation speed slows down.

By studying sea corals, oceanologists have found that a few billion years ago, the earth's day was twenty-two hours. In the future, the rotation of the Earth will slow down even more, and at some point it will simply equal the amplitude of the lunar day. In this case, as scientists predict, the ebb and flow will simply disappear.

Human activity and the amplitude of oscillations of the World Ocean

It is not surprising that a person is also susceptible to the action of hot flashes. After all, it is 80% liquid and cannot but respond to the influence of the moon. But man would not have been the crown of nature's creation if he had not learned to use practically everything for himself. natural phenomena.

The energy of the tidal wave is incredibly high, so for many years various projects have been created for the construction of power plants in areas with a large amplitude of movement of water masses. There are already several such power plants in Russia. The first was built in the White Sea and was an experimental version. The power of this station did not exceed eight hundred kilowatts. Now the figure seems ridiculous, and new power plants using the tidal wave are generating energy that powers many cities.

Scientists see these projects as the future of the Russian energy industry, because they allow them to treat nature more carefully and cooperate with it.

The ebb and flow are natural phenomena that not so long ago were completely unexplored. Each new discovery by oceanologists leads to even greater questions in this area. But perhaps someday scientists will be able to unravel all the secrets that the ocean tide presents to mankind every day.

Let's continue talking about the forces acting on celestial bodies and the resulting effects. Today I will talk about tides and non-gravitational disturbances.

What does this mean - "non-gravitational disturbances"? Perturbations are usually called small corrections to a large, main force. That is, we will talk about some forces, the influence of which on the object is much less than gravitational

What other forces are there in nature besides gravity? We leave aside strong and weak nuclear interactions, they are local in nature (they act at extremely small distances). But electromagnetism, as you know, is much stronger than gravity and spreads just as far - infinitely. But since electric charges opposite signs are usually balanced, and the gravitational "charge" (the role of which is played by mass) is always of the same sign, then with sufficiently large masses, of course, gravity comes to the fore. So in reality we will talk about disturbances in the motion of celestial bodies under the action electromagnetic field... There are no more options, although there are still dark energy, but more about it later, when it comes to cosmology.

As I told you on, Newton's simple law of gravitation F = G∙M∙m/R² is very convenient to use in astronomy, because most bodies are close to spherical and are sufficiently distant from each other, so that when calculating they can be replaced by points - point objects containing their entire mass. But a body of finite size, comparable to the distance between neighboring bodies, nevertheless, experiences a different force effect in its different parts, because these parts are differently removed from the sources of gravity, and this must be taken into account.

Attraction flattens and tears

To experience the tidal effect, let's do a thought experiment popular with physicists: imagine ourselves in a freely falling elevator. Cut off the rope holding the booth and begin to fall. Until we fall, we can watch what is happening around us. We suspend the free masses and watch how they behave. First, they fall synchronously, and we say - this is weightlessness, because all objects in this cabin and it itself feel about the same acceleration of gravity.

But over time, our material points will begin to change their configuration. Why? Because the lower one at the beginning was slightly closer to the center of gravity than the upper one, so the lower one, attracting more strongly, begins to outstrip the upper one. And the lateral points always remain at the same distance from the center of gravity, but as they approach it, they begin to approach each other, because accelerations of equal magnitude are not parallel. As a result, the system of unrelated objects is deformed. This is called the tidal effect.

From the point of view of an observer who has scattered cereals around him and watches how individual grains move while this whole system falls on a massive object, one can introduce such a concept as a field of tidal forces. Let us define these forces at each point as the vector difference between the gravitational acceleration at this point and the acceleration of the observer or the center of mass, and if we take only the first term of the expansion in the Taylor series in terms of relative distance, we get a symmetric picture: the near grains will be ahead of the observer, the far ones will lag behind him, i.e. the system will stretch along the axis directed to the gravitating object, and along the directions perpendicular to it, the particles will be pressed against the observer.

What do you think will happen when a planet is pulled into a black hole? Those who have not listened to lectures on astronomy usually think that a black hole will tear off matter only from the surface facing itself. Unbeknownst to them, the effect is almost as strong on the reverse side of a freely falling body. Those. it breaks in two diametrically opposite directions, by no means in one.

The dangers of outer space

To show how important it is to take into account the tidal effect, let us take the International space station... She, like all satellites of the Earth, freely falls in the gravitational field (if the engines are not turned on). And the field of tidal forces around it is quite a tangible thing, so when an astronaut works on the outer side of the station, he must tie himself to it, and, as a rule, with two cables - just in case, you never know what might happen. And if he turns out to be unattached in those conditions where tidal forces are pulling him away from the center of the station, he can easily lose contact with it. This often happens with tools, because you can't tie all of them. If something falls out of the hands of an astronaut, then this object goes into the distance and becomes an independent satellite of the Earth.

The plan of work on the ISS includes tests in open space of an individual jetpack... And when his engine fails, the tidal forces carry the astronaut away, and we lose him. The names of the missing are classified.

This, of course, is a joke: fortunately, there has not been such an incident yet. But this could very well have happened! And it might happen someday.

Ocean planet

Let's go back to Earth. This is the most interesting object for us, and the tidal forces acting on it are felt quite noticeably. From which celestial bodies do they act? The main one is the Moon, because it is close. The next largest impact is the Sun, because it is massive. The rest of the planets also have some influence on the Earth, but it is barely perceptible.

To analyze the external gravitational influence on the Earth, it is usually represented as a solid sphere covered with a liquid shell. This is not a bad model, since our planet does have a movable shell in the form of an ocean and an atmosphere, and everything else is pretty solid. Although the earth's crust and inner layers have limited rigidity and are slightly tidal, their elastic deformation can be neglected when calculating the effect produced on the ocean.

If we draw the vectors of tidal forces in the Earth's center of mass system, we get the following picture: the tidal force field pulls the ocean along the "Earth-Moon" axis, and in the plane perpendicular to it pushes it to the center of the Earth. Thus, the planet (in any case, its movable shell) tends to take the shape of an ellipsoid. In this case, two bulges appear (they are called tidal humps) on opposite sides of the globe: one faces the Moon, the other from the Moon, and a “bulge” appears in the strip between them (more precisely, the ocean surface has a lower curvature there).

A more interesting thing happens in the gap - where the tidal force vector tries to displace the liquid shell along the earth's surface. And this is natural: if in one place you want to raise the sea, and in another place - to lower it, then you need to move the water from there to here. And between them, tidal forces drive water to the "sublunar point" and to the "anti-lunar point".

It is very easy to quantify the tidal effect. The gravity of the Earth tries to make the ocean spherical, and the tidal part of the lunar and solar influence- stretch it along the axis. If we left the Earth alone and allowed it to freely fall on the Moon, then the height of the bulge would reach about half a meter, i.e. the ocean rises only 50 cm above its average level. If you are sailing on a steamboat open sea or the ocean, half a meter - it is not perceptible. This is called static tide.

In almost every exam I come across a student who confidently claims that the tide occurs only on one side of the Earth - the one that faces the Moon. As a rule, this is what a girl says. But it happens, although less often, that young men are mistaken in this matter. At the same time, in general, the knowledge of astronomy is deeper among girls. It would be interesting to find out the reason for this "tidal-gender" asymmetry.

But in order to create a half-meter bulge at the sublunary point, you need to distill a large amount of water here. But the surface of the Earth does not remain stationary, it rotates rapidly in relation to the direction to the Moon and the Sun, making full turn per day (and the Moon is slowly orbiting - one revolution around the Earth in almost a month). Therefore, the tidal hump constantly runs along the surface of the ocean, so that the solid surface of the Earth is under the tidal bulge 2 times per day and 2 times under the ebb and flow of the ocean level. Let's estimate: 40 thousand kilometers (the length of the earth's equator) per day, that's 463 meters per second. This means that this half-meter wave, such as a mini-tsunami, runs on the eastern coasts of the continents in the equatorial region at supersonic speed. At our latitudes, the speed reaches 250-300 m / s - also quite a lot: although the wave is not very high, due to inertia it can create a great effect.

The second object in terms of the scale of influence on the Earth is the Sun. It is 400 times farther from us than the Moon, but 27 million times more massive. Therefore, the effects from the Moon and from the Sun are comparable in magnitude, although the Moon still acts a little stronger: the gravitational tidal effect from the Sun is about half weaker than from the Moon. Sometimes their influence adds up: this happens on a new moon, when the moon passes against the background of the sun, and on a full moon, when the moon is on the opposite side from the sun. These days - when the Earth, Moon and Sun line up, and this happens every two weeks - the total tidal effect is one and a half times greater than from the Moon alone. And after a week, the Moon passes a quarter of its orbit and is in square with the Sun (a right angle between the directions on them), and then their influence weakens each other. On average, the height of tides on the high seas varies from a quarter of a meter to 75 centimeters.

Tides have been known to sailors for a long time. What does the captain do when the ship runs aground? If you have read marine adventure novels, then you know that he immediately looks at what phase the moon is in, and waits for the next full moon or new moon. Then the maximum tide can lift the ship and drive it aground.

Coastal issues and features

The tides are especially important for port workers and for seafarers who intend to bring their ship into or out of port. As a rule, the problem of shallow water arises near the coast, and so that it does not interfere with the movement of ships, to enter the bay, they break through underwater channels - artificial fairways. Their depth should take into account the height of the maximum low tide.

If we look at the height of the tides at some point in time and draw lines on the map equal height water, you get concentric circles with centers at two points (in the sublunar and anti-lunar), in which the tide is maximum. If the orbital plane of the Moon coincided with the plane of the Earth's equator, then these points would always move along the equator and in a day (more precisely, in 24ʰ 50ᵐ 28ˢ) would make a complete revolution. However, the Moon walks not in this plane, but near the plane of the ecliptic, with respect to which the equator is tilted by 23.5 degrees. Therefore, the sublunary point "walks" also in latitude. Thus, in the same port (i.e., at the same latitude), the height of the maximum tide, which repeats every 12.5 hours, changes during the day depending on the orientation of the Moon relative to the Earth's equator.

This "little thing" is important for the theory of tides. Let's look again: the Earth rotates on its axis, and the plane of the lunar orbit is inclined to it. Therefore, each seaport "runs" around the Earth's pole during the day, once falling into the area of ​​the highest tide, and after 12.5 hours - again into the area of ​​the tide, but less high. Those. two tides during the day are not equal in height. One is always larger than the other, because the plane of the lunar orbit does not lie in the plane of the earth's equator.

For coastal residents, the tidal effect is vital. For example, in France there is one, which is connected to the mainland by an asphalt road laid along the bottom of the strait. There are many people living on the island, but they cannot use this road as long as the sea level is high. This road can only be traveled twice a day. People drive up and wait for the low tide when the water level drops and the road becomes accessible. People commute to and from work to and from the coast using a special tide chart that is published for everyone. settlement coast. If this phenomenon is not taken into account, water along the way can overwhelm a pedestrian. Tourists just come there and walk to look at the bottom of the sea when there is no water. A locals Something is collected from the bottom, sometimes even for food, i.e. in fact, this effect feeds people.

Life came out of the ocean thanks to the ebb and flow. As a result of the low tide, some coastal animals found themselves on the sand and had to learn to breathe oxygen directly from the atmosphere. If it were not for the Moon, then life, perhaps, would not so actively leave the ocean, because it is good there in all respects - a thermostated environment, weightlessness. But if you suddenly hit the shore, you had to somehow survive.

The coast, especially if it is flat, is strongly exposed at low tide. And for some time people lose the opportunity to use their floating craft, helplessly lying like whales on the shore. But there is something useful in this, because the low tide period can be used to repair ships, especially in some bay: the ships sailed, then the water left, and they can be repaired at this time.

For example, there is a Bay of Fundy on the east coast of Canada, which is said to have the highest tides in the world: the water level drop can reach 16 meters, which is considered a record for a sea tide on Earth. Sailors have adapted to this property: at high tide they bring the ship to the shore, strengthen it, and when the water leaves, the ship hangs, and it can be caulked up the bottom.

For a long time, people began to monitor and regularly record the moments and characteristics of high tides in order to learn how to predict this phenomenon. Soon invented tide gauge- a device in which the float moves up and down depending on sea level, and the readings are automatically drawn on paper in the form of a graph. By the way, the measuring instruments have hardly changed from the moment of the first observations to the present day.

Based on a large number of hydrographic records, mathematicians try to create a theory of tides. If you have a long-term record of a periodic process, you can decompose it into elementary harmonics - different amplitudes of a sinusoid with multiple periods. And then, having determined the parameters of the harmonics, extend the total curve into the future and, on this basis, make tide tables. Now such tables are published for every port on Earth, and any captain who is about to enter the port takes a table for him and looks when there will be a sufficient water level for his ship.

The most famous story associated with predictive calculations occurred in the Second world war: in 1944, our allies - the British and Americans - were going to open a second front against Hitlerite Germany, for this it was necessary to land on the French coast. The northern coast of France is very unpleasant in this respect: the coast is steep, 25-30 meters high, and the ocean bottom is rather shallow, so that ships can approach the coast only at moments maximum tides... If they ran aground, they would simply be shot with cannons. To avoid this, a special mechanical (electronic were not yet available) computing machine was created. She performed a Fourier analysis of sea level time series using drums rotating at their own speed, through which a metal cable passed, which summed up all the terms of the Fourier series, and a feather connected to the cable wrote out a graph of the tide height versus time. This was a top secret work that greatly advanced the theory of tides, because it was possible to predict the moment of the highest tide with sufficient accuracy, thanks to which heavy military transport ships sailed across the Channel and landed troops ashore. So mathematicians and geophysicists have saved the lives of many people.

Some mathematicians try to generalize the data on a planetary scale, trying to create a unified theory of tides, but it is difficult to compare records taken in different places, because the Earth is very wrong. It is only in a zero approximation that a single ocean covers the entire surface of the planet, but in fact there are continents and several weakly connected oceans, and each ocean has its own frequency of natural oscillations.

Previous discussions about sea level fluctuations under the influence of the Moon and the Sun concerned open ocean spaces, where tidal acceleration varies greatly from one coast to another. And in local bodies of water - for example, lakes - can the tide create a noticeable effect?

It would seem that there should not be, because at all points of the lake the tidal acceleration is approximately the same, the difference is small. For example, in the center of Europe there is Lake Geneva, it is only about 70 km long and has nothing to do with the oceans, but people have long noticed that there are significant daily fluctuations in water. Why do they arise?

Yes, the tidal force is extremely small. But the main thing is that it is regular, i.e. acts periodically. All physicists know the effect that, with periodic action of force, sometimes causes an increased amplitude of oscillations. For example, you take a bowl of soup in the dining room and. This means that the frequency of your steps is in resonance with the natural vibrations of the liquid in the tray. Noticing this, we abruptly change the pace of walking - and the soup "calms down". Each body of water has its own basic resonant frequency. And what bigger size reservoir, the lower the frequency of natural oscillations of the liquid in it. So, at Lake Geneva, its own resonant frequency turned out to be a multiple of the frequency of the tides, and a small tidal influence "blurs" Lake Geneva so that the level on its shores changes quite noticeably. These standing waves long period, arising in confined reservoirs, are called seiches.

Energy of the tides

Nowadays, they are trying to associate one of the alternative energy sources with the tidal effect. As I said before, the main effect of tides is not that the water rises and falls. The main effect is a tidal current, which drives water around the entire planet in a day.

In shallow places, this effect is very important. In the area of ​​New Zealand, captains do not even risk escorting ships through some straits. The sailing ships never made it through there, and modern ships pass with difficulty, because the bottom is shallow and the tidal currents have tremendous speed.

But once the water is flowing, this kinetic energy can be used. And power plants have already been built, in which the turbines rotate back and forth due to the tidal and ebb flow. They are quite workable. The first tidal power plant (TPP) was made in France, it is still the largest in the world, with a capacity of 240 MW. Compared to the hydroelectric power station, it is not so hot, of course, but it serves the nearest rural areas.

The closer to the pole, the lower the speed of the tidal wave, therefore in Russia there are no coasts with very powerful tides. In general, we have few outlets to the sea, and the coast of the Arctic Ocean for using tidal energy is not particularly profitable because the tide drives water from east to west. Still, there are places suitable for PES, for example, the Kislaya lip.

The fact is that in bays the tide always creates a greater effect: a wave runs in, rushes into the bay, and it narrows, narrows - and the amplitude increases. A similar process occurs as if the whip were flicked: first long wave goes slowly along the whip, but then the mass of the part of the whip involved in the movement decreases, therefore the speed increases (impulse mv persists!) and reaches the supersonic end to the narrow end, as a result of which we hear a click.

Creating an experimental Kislogubskaya TPP of small capacity, power engineers tried to understand how efficiently the tides in the circumpolar latitudes can be used to generate electricity. It has no particular economic meaning. However, now there is a project of a very powerful Russian TPP (Mezenskaya) - 8 gigawatts. In order to achieve this colossal capacity, it is necessary to block off a large bay, separating the White Sea from the Barents Sea by a dam. True, it is highly doubtful that this will be done as long as we have oil and gas.

Past and future of the tides

By the way, where does the energy of the tides come from? The turbine is spinning, electricity is being generated, and which object is losing energy?

Since the source of energy for the tide is the rotation of the Earth, then since we draw from it, then the rotation should slow down. It would seem that the Earth has internal sources energy (heat from the bowels comes due to geochemical processes and the decay of radioactive elements), there is something to compensate for the loss of kinetic energy. It is, but energy flow, propagating on average almost uniformly in all directions, can hardly significantly affect the angular momentum and change the rotation.

If the Earth did not rotate, the tidal humps would point exactly in the direction of the Moon and in the opposite direction. But, rotating, the Earth's body carries them forward in the direction of its rotation - and there is a constant discrepancy between the tidal peak and the sublunary point of 3-4 degrees. What does this lead to? The hump, which is closer to the moon, is attracted to it more strongly. This gravity tends to slow down the Earth's rotation. And the opposite hump is farther from the Moon, it tries to accelerate the rotation, but is attracted weaker, therefore the resultant moment of forces has a braking effect on the Earth's rotation.

So, our planet is constantly decreasing its rotation speed (albeit not quite regularly, in jumps, which is associated with the peculiarities of mass transfer in the oceans and the atmosphere). And what is the impact of the earth's tides on the moon? The near tidal bulge pulls the moon with it, the distant one, on the contrary, slows it down. The first force is greater; as a result, the Moon is accelerating. Now, remember from the previous lecture, what happens to a satellite that is forcibly pulled forward in motion? As its energy increases, it moves away from the planet and its angular velocity decreases at the same time, because the radius of its orbit increases. By the way, an increase in the period of the Moon's revolution around the Earth was noticed back in the time of Newton.

In terms of numbers, the Moon is moving away from us by about 3.5 cm per year, and the duration of the Earth's day every hundred years increases by a hundredth of a second. It seems to be nonsense, but remember that the Earth has been around for billions of years. It is easy to calculate that in the days of the dinosaurs there were about 18 hours in a day (the current hours, of course).

As the moon recedes, the tidal forces become smaller. But it was always moving away, and if we look back in time, we will see that earlier the Moon was closer to the Earth, which means that the tides were higher. You can estimate, for example, that in the Archean era, 3 billion years ago, the tides were one kilometer high.

Tidal phenomena on other planets

Of course, in the systems of other planets with satellites, the same phenomena occur. Jupiter, for example, is a very massive planet with a large number of satellites. Its four largest moons (they are called Galilean, because Galileo discovered them) are influenced by Jupiter quite tangibly. The nearest of them, Io, is entirely covered with volcanoes, among which there are more than fifty active ones, and they throw out "excess" matter 250-300 km up. This discovery was quite unexpected: there are no such powerful volcanoes on Earth, but here is a small body the size of the Moon, which should have cooled down for a long time, but instead it glows with heat in all directions. Where is the source of this energy?

Io's volcanic activity was not a surprise to everyone: six months before the first probe flew to Jupiter, two American geophysicists published a paper in which they calculated the tidal influence of Jupiter on this moon. It turned out to be so large that it can deform the satellite's body. And with deformation, heat is always released. When we take a piece of cold plasticine and begin to crumple it in our hands, it becomes soft, pliable after several squeezes. This happens not because the hand has heated it with its heat (it will be the same if you flatten it in a cold vice), but because the deformation has put mechanical energy into it, which has been converted into heat.

But why on earth is the shape of the satellite changing under the influence of the tides from Jupiter? It would seem that moving in a circular orbit and rotating synchronously, like our Moon, once became an ellipsoid - and there is no reason for further distortions of the shape? However, there are other satellites near Io; all of them make his (Io) orbit shift a little back and forth: it either approaches Jupiter or recedes. This means that the tidal influence either weakens or intensifies, and the shape of the body changes all the time. By the way, I have not yet talked about the tides in solid body Lands: they, of course, also exist, they are not so high, of the order of a decimeter. If you sit for about six hours in your places, then thanks to the tides, you will "walk" about twenty centimeters relative to the center of the Earth. This oscillation is imperceptible for a person, of course, but geophysical instruments register it.

Unlike the earth's solid, Io's surface fluctuates with an amplitude of many kilometers for each orbital period. A large number of deformation energy is dissipated in the form of heat and heats the bowels. By the way, meteorite craters are not visible on it, because volcanoes constantly throw fresh matter on the entire surface. As soon as an impact crater forms, in a hundred years the products of the eruption of neighboring volcanoes fall asleep. They work continuously and very powerfully, to this are added faults in the planet's crust, through which melt of various minerals flows from the depths, mainly sulfur. At high temperatures, it darkens, so the jet from the crater looks black. And the light rim of the volcano is the cooled substance that falls around the volcano. On our planet, matter ejected from a volcano is usually slowed down by air and falls close to the vent, forming a cone, but on Io there is no atmosphere, and it flies along a ballistic trajectory far in all directions. This is perhaps the most powerful tidal effect in the solar system.

The second moon of Jupiter, Europa looks like our Antarctica, it is covered with a continuous ice crust, cracked here and there, because something is constantly deforming it too. Since this moon is farther from Jupiter, the tidal effect is not so strong here, but it is also quite noticeable. Beneath this ice crust there is a liquid ocean: the pictures show fountains gushing from some of the open cracks. Under the influence of tidal forces, the ocean boils, and ice fields float and collide on its surface, almost like we have in the North Arctic Ocean and off the coast of Antarctica. The measured electrical conductivity of the Europa ocean fluid indicates that it is salt water. Why shouldn't there be life? It would be tempting to lower the device into one of the cracks and see who lives there.

In fact, not all planets make ends meet. For example, Enceladus, the moon of Saturn, also has an ice crust and an ocean below it. But calculations show that the energy of the tides is not enough to support the sub-ice ocean in liquid state... Of course, except for the tides of anyone celestial body there are other sources of energy - for example, decaying radioactive elements (uranium, thorium, potassium), but on small planets they can hardly play a significant role. This means that we do not understand something yet.

The tidal effect is extremely important for stars. Why - more on that in the next lecture.