In which they discovered that the earth is round. earth formation

They say that this is...

However, the hypothesis that our planet is spherical has existed for a very long time. This idea was first expressed in the 6th century BC by the ancient Greek philosopher and mathematician Pythagoras. Another philosopher, Aristotle, who lived in Ancient Greece two centuries later, he gave clear evidence of sphericity: after all, during lunar eclipses, the Earth casts a shadow of exactly a round shape on the Moon!

Gradually, the idea that the Earth is a ball hanging in space and not relying on anything spread more and more widely. Centuries have passed, people have long known that the Earth is not flat and does not rest on whales or elephants ... We went around the world, crossed our ball literally in all directions, flew around it on an airplane, photographed from space. We even know why not only ours, but also all other planets, and the Sun, and the stars, and the Moon, and other large satellites are precisely “round”, and not of any other shape. After all, they are large, have a huge mass. Their own gravitational force - gravity - tends to give the celestial bodies the shape of a ball.

Even if some force appeared, greater than gravity, which would give the Earth the shape of, say, a suitcase, it would still end up the same: as soon as the action of this force ceased, the force of gravity would begin to collect the Earth into a ball again, “pulling” protruding parts, until all points of the surface are at an equal distance from the center.

Let's keep thinking about this...

Not a ball!

Back in the 17th century, the famous physicist and mathematician Newton made a bold assumption that the Earth is not a ball at all, or rather, not quite a ball. Assumed - and mathematically proved it.

Newton "drilled" (of course, mentally!) to the center of the planet two communicating channels: one from the North Pole, the other from the equator, and "filled" them with water. Calculations showed that the water settled at different levels. After all, in a polar well, only gravity acts on water, and in an equatorial well, centrifugal force still opposes it. The scientist argued that in order for both columns of water to exert the same pressure on the center of the Earth, that is, for them to have equal weight, the water level in the equatorial well should have been higher - according to Newton's calculations, by 1/230 of the average radius of the planet. In other words, the distance from the center to the equator is greater than to the pole.

To check Newton's calculations, the Paris Academy of Sciences sent two expeditions in 1735-1737: to Peru and to Lapland. The members of the expedition had to measure the arcs of the meridian - 1 degree each: one - in the equatorial latitudes, in Peru, the other - in the polar latitudes, in Lapland. After processing the expedition data, the leader of the northern one, surveyor Pierre-Louis Maupertuis, announced that Newton was right: the Earth is compressed at the poles! This discovery of Maupertuis was immortalized by Voltaire in ... an epigram:

Messenger of physics, brave sailor,

Overcoming mountains and seas.

Dragging a quadrant in the midst of snow and swamps,

Almost turned into a lopar.

You learned after many losses.

What Newton knew without leaving the door.

In vain Voltaire was so caustic: how can science exist without experimental confirmation of its theories?!

Be that as it may, now we know for sure that the Earth is flattened at the poles (if you like, stretched at the equator). It is stretched, however, quite a bit: the polar radius is 6357 km, and the equatorial one is 6378 km, only 21 km more.

Looks like a pear?

However, is it possible to call the Earth, if not a ball, but an “oblate” ball, namely, an ellipsoid of revolution? After all, as we know, its relief is uneven: there are mountains, there are also depressions. In addition, it is affected by the forces of attraction of other celestial bodies, primarily the Sun and the Moon. Let their influence be small, but still the Moon is capable of bending the shape of the liquid shell of the Earth - the World Ocean - by several meters, creating ebbs and flows. So - at different points, the radii of "rotation" are different!

In addition, in the north there is a "liquid" ocean, and in the south - a "solid" continent covered with ice - Antarctica. It turns out that the Earth has not quite the correct shape, it resembles a pear, elongated to the North Pole. And by and large, its surface is so complex that it does not lend itself to a strict mathematical description at all. Therefore, scientists have proposed a special name for the shape of the Earth - the geoid. The geoid is an irregular stereometric figure. Its surface approximately coincides with the surface of the World Ocean and continues on the mainland. The same “altitude above sea level”, which is indicated in atlases and dictionaries, is measured precisely from this geoid surface.

Well, scientifically:

Geoid(from other Greek γῆ - Earth and other Greek εἶδος - view, literally - “something like the Earth”) - a convex closed surface coinciding with the surface of the water in the seas and oceans in a calm state and perpendicular to the direction of gravity at any point in it. Geometric body deviating from the figure of revolution Ellipsoid of revolution and reflecting the properties of the gravity potential on the Earth (near earth's surface), an important concept in geodesy.

1. World Ocean

2. Earth ellipsoid

3. Sheer lines

4. Body of the Earth

The geoid is defined as the equipotential surface of the earth's gravity field (level surface), approximately coinciding with the average water level of the World Ocean in an undisturbed state and conditionally continued under the continents. The difference between the real mean sea level and the geoid can reach 1 m.

By definition of an equipotential surface, the surface of the geoid is perpendicular to the plumb line everywhere.

A geoid is not a geoid!

To be completely honest, it is worth admitting that due to the difference in temperature in different parts of the planet and the salinity of the oceans and seas, atmospheric pressure and other factors, the surface of the water surface does not even coincide in shape with the geoid, but has deviations. For example, at the latitude of the Panama Canal, the difference between the levels of the Pacific and Atlantic oceans is 62 cm.

Strong earthquakes also affect the shape of the globe. One such 9-magnitude earthquake occurred on December 26, 2004 in South-East Asia, in Sumatra. University of Milan professors Roberto Sabadini and Giorgio Dalla Via believe that it left a "scar" on the planet's gravitational field, causing the geoid to sag significantly. To test this assumption, the Europeans intend to send a new GOCE satellite into orbit, equipped with modern highly sensitive equipment. We hope that soon he will send us accurate information about the shape of the Earth today.

and a little more interesting about the Earth: for example, when did you find out that the Earth is round? or When the Earth was first photographed from space. But you know, for example, Why are the continents and parts of the world called so? and it was recently reported that

+
Original taken from masterok in
Long-lost continent found at the bottom of the Indian Ocean

In early 2013, geologists found evidence that under the ocean, between Madagascar and India, the submerged remains of an ancient microcontinent are scattered.

The proof was a find in Mauritius - a volcanic island lying about 900 km east of Madagascar. The oldest basalts there are about 8.9 million years old, says geologist Bjorn Jamtveit from the University of Oslo (Norway). But a careful analysis of sand from two local beaches revealed about twenty zircons - zirconium silicate crystals that are highly resistant to erosion and chemical changes. They are much older.

These zircons were formed in granites and other volcanic rocks at least 660 million years ago. One of the crystals is at least 1.97 billion years old.

Mr. Yamtveit and his colleagues suggest that the rocks containing these zircons originated in fragments of ancient continental crust under Mauritius. It seems that relatively recent volcanic eruptions have brought fragments of the crust to the surface, where the zircons have been eroded into the sand.

Researchers also suspect that under the bottom indian ocean lies many fragments of that continental crust. An analysis of the Earth's gravitational field has revealed several areas where the oceanic crust is much thicker than usual - 25–30 km instead of the usual 5–10 km.

This anomaly may be the remnants of the land, which scientists propose to call Mauritia (Mauritia). It likely split from Madagascar when tectonic rifting and stretching of the seafloor caused the Indian subcontinent to move from the southern Indian Ocean in a northeasterly direction. The subsequent stretching and thinning of the crust in this area led to the subsidence of fragments of Mauritia, which at that time consisted of an island or archipelago with a total area of \u200b\u200babout three Cretes.

The scientists chose sand, rather than local rocks, to analyze, to ensure that zircons that were inadvertently stuck in crushing equipment from previous studies did not contaminate fresh samples.

“We found zircon in the sand,” says University of Oslo professor Trond Torsvik, who led the study, “which is normally found in continental crust. Moreover, the zircons we found are very, very ancient.”

The nearest outcrop of continental crust where Mauritian zircons can still be found is deep underwater. In addition, zircons were mined in places in Mauritius where people almost never go and could hardly bring them with them. At the same time, the crystals are too large to be carried there by the wind.

Approximately 85 million years ago, the BBC quoted Professor Torsvik as saying, when India began to separate from Madagascar, the microcontinent broke down and went under water. Only minor remnants of it have survived, for example, the Seychelles.

“We need data of a seismological nature to get information about the geological structure of the rock at the bottom of the ocean,” Professor Torsvik explained.

“Or you can start excavations at the bottom of the ocean, but it will cost enormous money,” he stressed.

Rodinia is a supercontinent believed to have formed about a billion years ago. At that time, the Earth consisted of one giant piece of land and one giant ocean. Rodinia is considered the oldest known supercontinent, but its position and outlines are still the subject of controversy among scientists and experts.

Here is the most common version:

Once upon a time we could (if we lived at that time, of course) walk from Australia to North America. Many beings living at that time made such transitions more than once. While heavy iron-bearing rocks sank deeper, forming a core over several hundred million years, light stony rocks, rising to the surface, formed a crust. Gravitational contraction and radioactive decay further heated the interior of the Earth. In connection with the increase in temperature from the surface to the center of our planet, foci of tension arose at the boundary with the crust (where the convective rings of mantle matter converge into an upward flow.)

Under the influence of mantle currents, lithospheric plates are in constant motion, hence volcanoes, earthquakes and continental drift arise. The continents are constantly moving relative to each other, but since the rate of their displacement is about 1 centimeter per year, we do not notice this movement. Nevertheless, if we compare the positions of the continents in billions of years, the shifts become tangible. The theory of continental drift was first put forward in 1912 by the German geographer Alfred Wegener, when he noticed that the borders of Africa and South America are similar, like pieces of the same mosaic. Later, after exploring the bottom of the ocean, his theory was confirmed. In addition, it was concluded that the North and South magnetic poles have changed places 16 times over the past 10 million years! Our planet was formed gradually: much that was before disappeared, and now there is something that was absent in the past. Not immediately free oxygen appeared on the planet. Before the Proterozoic, despite the fact that there was already life on the planet, the atmosphere consisted only of carbon dioxide, hydrogen sulfide, methane and ammonia. Scientists have found the oldest deposits, clearly not subjected to oxidation.

For example, river pebbles from pyrite, which reacts well with oxygen. If this did not happen, then there was no oxygen by that time. In addition, 2 billion years ago, there were no potential sources capable of producing oxygen at all. To this day, photosynthetic organisms are the only source of oxygen in the atmosphere. At the beginning of the Earth's history, the oxygen produced by Archean anaerobic microorganisms was almost immediately spent on the oxidation of dissolved compounds, rocks and gases in the atmosphere. Molecular oxygen was almost non-existent; by the way, it was poisonous to most of the organisms that existed at that time. By the beginning of the Paleoproterozoic era, all surface rocks and gases in the atmosphere had already been oxidized, and oxygen remained in the atmosphere in a free form, which led to an oxygen catastrophe. Its significance is that it has globally changed the position of communities on the planet.

If earlier most of the Earth was inhabited by anaerobic organisms, that is, those that do not need oxygen and for which it is poisonous, now these organisms have faded into the background. The first place was taken by those who used to be in the minority: aerobic organisms, which previously existed only in a negligible space of accumulation of free oxygen, were now able to "settle" throughout the planet, with the exception of those small areas where there was not enough oxygen. An ozone screen formed over the nitrogen-oxygen atmosphere, and cosmic rays almost stopped penetrating the Earth's surface. The consequence of this is a decrease in the greenhouse effect and global climate change. 1.1 billion years ago, there was one giant continent on our planet - Rodinia (from Russian Rodina) and one ocean - Mirovia (from Russian world). This period is called the "Ice World", as it was very cold on our planet at that time. Rodinia is considered the oldest continent on the planet, but there are suggestions that other continents existed before it.

Rodinia broke up 750 million years ago, apparently due to upward heat flows in the Earth's mantle, which blew up areas of the supercontinent, stretching the crust and causing it to break in those places. Although living organisms existed before the break of Rodinia, but only in Cambrian period animals began to appear with a mineral skeleton that came to replace soft bodies. This time is sometimes called the "Cambrian explosion", at the same moment the next supercontinent - Pangea (Greek Πανγαία - all-earth) was formed. Most recently, 150-220 million years ago (and for the Earth this is a very insignificant age), Pangea broke up into Gondwana, "collected" from modern South America, Africa, Antarctica, Australia and the Hindustan island, and Laurasia - the second supercontinent, consisting of Eurasia and North America. After tens of millions of years, Laurasia split into Eurasia and North America, which, as you know, exist to this day. And after another 30 million years, Gondwana split into Antarctica, Africa, South America, Australia and India, which is a subcontinent, that is, it has its own continental plate. The movement of the continents continues to this day.

Presumably, our continents will collide again and form a new supercontinent, which has already been given a name - Pangea Ultima. The term Pangea Ultima and the very theory of the appearance of the mainland were invented by the American geologist Christopher Scotese, who, using various methods calculation of the movement of lithospheric plates, found that the merger could occur somewhere in 200 million years. The last Pangea, as this continent is sometimes called in Russia, will be almost entirely covered with deserts, and in the northwest and southeast there will be huge mountain ranges. .

The fact that the shape of our planet is spherical, people did not immediately learn. Let's move smoothly back to ancient times, when people believed that the Earth was flat, and together with ancient thinkers, philosophers and travelers, let's try to come to the idea of the Earth's sphericity...

(This post is inspired by the thoughts of the author and blog guests to the post " How do I improve my skills in the course? Part 2: How cartoons can harm our children")

The ideas of our distant ancestors about the Earth were mainly based on myths, traditions and legends.

Ancient Greeks it was believed that the planet is a convex disk, similar to a warrior's shield, washed on all sides by the Ocean River.

In ancient China there was an idea according to which the Earth has the shape of a flat rectangle, above which a round, convex sky is supported on pillars. The enraged dragon seemed to bend the central pillar, as a result of which the Earth leaned towards the east. Therefore, all rivers in China flow to the east. The sky tilted to the west, so all the heavenly bodies move from east to west.

Greek philosopher Thales(VI century BC) represented the Universe in the form of a liquid mass, inside of which there is a large bubble, shaped like a hemisphere. The concave surface of this bubble is the vault of heaven, and on the lower, flat surface, like a cork, the flat Earth floats. It is easy to guess that Thales based the idea of the Earth as a floating island on the fact that Greece is located on islands.

A contemporary of Thales - Anaximander represented the Earth as a segment of a column or cylinder, on one of the bases of which we live. The middle of the Earth is occupied by land in the form of a large round island of Oikumene (" inhabited earth") surrounded by the ocean. Inside the Oikumene there is a sea basin that divides it into two approximately equal parts: Europe and Asia:

And here is the world in view ancient egyptians:

Below is the Earth, above it is the goddess of the sky;
on the left and on the right is the ship of the sun god, showing the path of the sun across the sky from sunrise to sunset.

ancient indians represented the Earth in the form of a hemisphere, based on elephants.

Elephants stand on the shell of a huge turtle standing on a snake and swimming in the endless ocean of milk. The snake, curled up in a ring, closes the near-Earth space.
Please note that the truth is still far away, but the first step towards it has already been taken!

Babylonians represented the Earth in the form of a mountain, on the western slope of which Babylonia is located.

They knew that there was a sea to the south of Babylon, and mountains to the east, which they did not dare to cross. Therefore, it seemed to them that Babylonia is located on the western slope of the "world" mountain. This mountain is surrounded by the sea, and on the sea, like an overturned bowl, the firm sky rests - the heavenly world, where, like on Earth, there is land, water and air.

BUT in Russia believed that the Earth is flat and rests on three whales that swim in the vast oceans of the world.

When people began to make long journeys, evidence gradually began to accumulate that the Earth was not flat, but convex.

The first assumption about the sphericity of the Earth said the ancient Greek philosopher Parmenides in the 5th century BC

But first evidence This was given by three ancient Greek scientists: Pythagoras, Aristotle and Eratosthenes.

Pythagoras said that the earth could not have any other form than a sphere. It can't - and that's it! Because, according to Pythagoras, everything in nature is arranged correctly and beautifully. And he considered the ball to be the most correct and therefore beautiful figure. Here is some kind of proof

Aristotle was very observant and smart person. Therefore, he managed to collect a lot of evidence of the sphericity of the Earth.
First: if you look at a ship approaching from the sea, then first masts will appear from behind the horizon, and only then - the hull of the ship.

But this proof did not satisfy many.

Second, the most serious evidence of Aristotle is related to the observations that he made during lunar eclipses.
At night, a huge shadow "runs" on the Moon, and the Moon "goes out", though not completely: it only darkens and changes color. The ancient Greeks said that the moon becomes "the color of dark honey."
In general, the Greeks believed that a lunar eclipse was a very dangerous phenomenon for health and life, so it took a lot of courage from Aristotle. He repeatedly observed lunar eclipses and realized that the huge shadow covering the Moon is the shadow of the Earth, which our planet casts when it is between the Sun and the Moon. Aristotle drew attention to one oddity: no matter how many times and at what time he observes a lunar eclipse, the shadow of the Earth is always round. But only one figure has a round shadow - the ball.
By the way, the next lunar eclipse will be... April 15, 2014.

In one source, I found such an interesting fragment with the words of Aristotle himself:

Three Proofs for the Earth's Sphericitywe find in Aristotle's book "On Heaven".

1. All heavy bodies fall to the ground at equal angles. This is the first Aristotelian proof of the sphericity of the Earth in need of explanation. The fact is that Aristotle believed that the heavy elements, among which he attributed earth and water, naturally tend to the center of the world, which therefore coincides with the center of the Earth. If the Earth were flat, then the bodies would not fall perpendicularly, because they would rush to the center of the flat Earth, but since all bodies cannot be directly above this center, then most bodies would fall to the earth along an inclined line.

2. But also (the sphericity of the Earth) follows from what is revealed to our senses. For, of course, the eclipses of the Moon would not have such a shape (if the Earth were flat). The defining line during (lunar) eclipses is always arcuate. So, due to the fact that the Moon is eclipsed due to the location of the Earth between it and the Sun, the shape of the Earth must be spherical. Here Aristotle relies on the teachings of Anaxagoras about the cause of solar and lunar eclipses.
3. Some of the stars are visible in Egypt and Cyprus, but are not visible in places located to the north. From this it is not only clear that the shape of the earth is spherical, but also that the earth is a sphere of small dimensions. This third proof of the sphericity of the Earth is based on observations made in Egypt by the ancient Greek mathematician and astronomer Eudoxus, who belonged to the Pythagorean union.

The third famous scientist was Eratosthenes. He was the first to find out the size of the globe, thereby once again proving that the Earth has the shape of a ball.

The ancient Greek mathematician, astronomer and geographer Erastofen of Cyrene (circa 276-194 BC) determined the size of the globe with amazing accuracy. Now we know that a day summer solstice(June 21-22), at noon, the Sun on the Tropic of Cancer (or Northern Tropic) is at its zenith, i.e. its rays fall vertically on the surface of the Earth. Erastofen knew that on this day the Sun illuminates the bottom of even the deepest wells in the vicinity of Siena (Siena- ancient name Aswan).

At noon, he measured the angle between the pillar and the rays of the sun in the shadow of a vertical pillar installed in Alexandria, 800 km from Siena (Erastofen made a device for measuring - skafis, a hemisphere with a rod casting a shadow) and found it equal to 7.2 o, which is 7.2 / 360 of a full circle, i.e. 800 km or 5,000 Greek stadia (1 stadia was approximately equal to 160 m, which is approximately equal to the modern 1 degree and, accordingly, 111 km). From this, Erastofen deduced that the length of the equator = 40,000 km (according to modern data, the length of the equator is 40,075 km).

Let's see what the textbook for fifth graders offers:

Feel like an ancient geographer!

Characteristic of this time are the views of the Byzantine geographer of the 6th century. Kosma Indikoplova. A merchant and trader, Cosmas Indikoples made long trade journeys through Arabia and East Africa. Having become a monk, Cosmas Indikoples compiled a number of descriptions of his travels, including the only Christian topography that has come down to us. He came up with his fantastic picture of the structure of the Earth. The earth seemed to him in the form of a rectangle, stretched from west to east.
Referring to the scripture, he established the ratio of its length to width - 2: 1. On all sides, the earth's rectangle is surrounded by the ocean, and along its edges there are high mountains, on which the heavenly vault rests. Stars move along the vault, which are moved by angels assigned to them. The sun rises in the east and hides at the end of the day behind the mountains in the west, and during the night passes behind the mountain located in the north of the Earth. Internal structure Kosma Indikoplova was not interested in the earth at all. They did not allow any changes in the relief of the Earth. Despite the obvious fantasticness, Indikoplov's cosmographic representations were very widespread in Western Europe, and later in Russia.

Nicholas Copernicus also contributed to the proof of the sphericity of the Earth.
He found that moving south, travelers see that in the southern side of the sky the stars rise above the horizon in proportion to the distance traveled, and new stars appear above the Earth that were not previously visible. And in the northern side of the sky, on the contrary, the stars descend towards the horizon and then completely disappear behind him.

In the Middle Ages, European geography, like many other sciences, enters a period of stagnation and rolls back in its development, incl. the fact of the sphericity of the Earth and the assumptions about the geolycentric model of the solar system are rejected. The main European navigators of that time - the Scandinavian Vikings - were not too interested in the problems of cartography, relying rather on their art of sailing on the waters of the Atlantic. Byzantine scientists considered the earth to be flat, Arab geographers and travelers did not have unambiguous views about the shape of the Earth, being primarily engaged in the study of peoples and cultures, rather than directly in physical geography.
Ignorant and religious fanatics brutally persecuted people who doubt that the Earth is flat and that it has an "end of the world" (and with the cartoon about Smeshariki, we seem to be returning to those days).

A new period of knowledge of the world begins at the end of the 15th century, this time is often called the era of the Great Geographical Discoveries. In 1519-1522 a Portuguese traveler Ferdinand Magellan(1480-1521) and his team make the first trip around the world, which in practice confirms the theory of the sphericity of the Earth.

August 10, 1519 five ships - "Trinidad", "San Antonio", "Concepción", "Victoria" and "Santiago" sail from Seville to circumnavigate the globe. Fernando Magellan was absolutely not sure of the happy end of the voyage, because the thought of the spherical shape of the Earth was only an assumption.
The journey ended successfully - it was proved that the Earth is round. Magellan himself did not live to return to his homeland - he died on the way. But before his death, he knew that his goal had been achieved.

Another proof sphericity can be observed that at sunrise, its rays first illuminate clouds and other high objects, the same process is observed during sunset.

Also is proof the fact that when you go up, your horizons increase. On a flat surface, a person sees around him for 4 km, at a height of 20 m it is already 16 km, from a height of 100 m the horizon expands by 36 km. At an altitude of 327 km, a space with a diameter of 4000 km can be observed.

One more proof sphericity is based on the assertion that all celestial bodies of our solar system have a spherical shape and the Earth in this case is no exception.

BUT photo evidence sphericity became possible after the launch of the first satellites, which took photographs of the Earth from all sides. And, of course, the first person who saw the whole Earth as a whole was Yuri Alekseevich Gagarin on 04/12/1961.

I think that the sphericity of the Earth is proved!!!

Do you agree?

When writing this article, materials from textbooks and atlases on geography were used (according to the new Federal State Educational Standards, geography from grade 5):
Geography. 5-6 cells Notebook-workshop_Kotlyar O.G_2012 -32s
Geography. 5-6 cells Alekseev A.I. and others_2012 -192s
Geography. 5 cells Atlas._Letyagin A.A_2013 -32s
Geography. 5 cells Introduction to geography. Domogatskikh E.M. and others_2013 -160s
Geography. 5 cells Initial course. Letyagin A.A_2013 -160s
Geography. 5 cells Planet Earth_Petrova, Maksimova_2012 -112s,
as well as Internet materials.

None of the sources used

DOES NOT INCLUDE ALL THE EVIDENCE DESCRIBED AT THE SAME TIME!

Who said the earth is round? December 17th, 2014

They say that this is...

However, the hypothesis that our planet is spherical has existed for a very long time. This idea was first expressed in the 6th century BC by the ancient Greek philosopher and mathematician Pythagoras. Another philosopher, Aristotle, who lived in ancient Greece two centuries later, provided clear evidence of sphericity: after all, during lunar eclipses, the Earth casts a shadow of a round shape on the Moon!

Let's keep thinking about this...

Not a ball!

Messenger of physics, brave sailor,
Overcoming mountains and seas.
Dragging a quadrant in the midst of snow and swamps,
Almost turned into a lopar.
You learned after many losses.
What Newton knew without leaving the door.

In vain Voltaire was so caustic: how can science exist without experimental confirmation of its theories?!

Looks like a pear?

Well, scientifically:

Geoid(from other Greek γῆ - Earth and other Greek εἶδος - view, literally - “something like the Earth”) - a convex closed surface coinciding with the surface of the water in the seas and oceans in a calm state and perpendicular to the direction of gravity at any point in it. A geometric body that deviates from a figure of revolution An ellipsoid of revolution and reflects the properties of the gravity potential on the Earth (near the earth's surface), an important concept in geodesy.

1. World Ocean
2. Earth ellipsoid
3. Sheer lines
4. Body of the Earth
5. Geoid

By definition of an equipotential surface, the surface of the geoid is perpendicular to the plumb line everywhere.

A geoid is not a geoid!

Strong earthquakes also affect the shape of the globe. One of these 9-magnitude earthquakes occurred on December 26, 2004 in Southeast Asia, in Sumatra. University of Milan professors Roberto Sabadini and Giorgio Dalla Via believe that it left a "scar" on the planet's gravitational field, causing the geoid to sag significantly. To test this assumption, the Europeans intend to send a new GOCE satellite into orbit, equipped with modern highly sensitive equipment. We hope that soon he will send us accurate information about the shape of the Earth today.

During the life of Columbus, people believed that the Earth was flat. They believed that in Atlantic Ocean huge monsters live, capable of swallowing their ships, and there are terrible waterfalls on which their ships will perish. Columbus had to fight these strange notions to convince people to go sailing with him. He was convinced that the earth was round.
— Emma Miler Bolenius, author of American textbooks, 1919

One of the longest-lived myths children grow up believing in [ author - American - approx.transl.], is that Columbus was the only one of the people of his time who believed that the Earth was round. The rest believed that she was flat. “How brave the navigators of 1492 must have been,” you think, “to go to the end of the world and not be afraid to fall off it!”

Indeed, there are many ancient references to the earth in the form of a disk. And if of all the celestial bodies only the Sun and the Moon were known to you, you could independently come to the same conclusion.

If you go outside at sunset, a day or two after the new moon, you can see something like this.

A thin crescent of the Moon, the illuminated part of which coincides with the part of the sphere that could be illuminated by the Sun.

If you had a scientific mind and curiosity, you could go out on the following days and watch what happens next.

Not only does the moon change position by about 12 degrees each night as it moves further away from the sun, it's getting brighter! You could (fairly) conclude that the Moon revolves around the Earth, and that the change in phases is due to the light from the Sun shining on different parts of the round Moon.

Ancient and modern views on the phases of the moon coincide in this.

But about twice a year during a full moon, something happens that allows us to determine the shape of the Earth: a lunar eclipse! During a full moon, the Earth passes between the Sun and the Moon, and the shadow of the Earth becomes visible on the surface of the Moon.

And if you look at this shadow, it becomes clear that it is bent and has the shape of a disk!

True, it cannot be deduced from this whether the Earth is a flat disk or a round sphere. One can only see that the Earth's shadow is round.

But, despite the popular myth, the question of the shape of the Earth was decided not in the 15th or 16th centuries (when Magellan made a trip around the world), but about 2000 years ago, in ancient world. And what is most surprising, for this it took only the Sun.

If you track the path of the Sun in the daytime sky while living in the northern hemisphere, you will notice that it rises in the eastern part of the sky, rises to a maximum in the south, and then declines and sets in the west. And so on any day of the year.

But the paths throughout the year are slightly different. The sun rises much higher and shines for more hours in summer, and rises lower and shines less in winter. For illustration, look at the photo of the solar path, taken during the winter solstice in Alaska.

If you plot the path of the Sun across the daytime sky, you will find that the lowest path, and the shortest in time, is at the winter solstice - usually December 21 - and the highest path (and longest) is at the summer solstice, usually 21 June.

If you make a camera capable of photographing the path of the Sun across the sky over the course of a year, you end up with a set of arcs, the highest and longest of which was taken on the summer solstice, and the lowest and shortest on the winter solstice.

In the ancient world, the greatest scholars of Egypt, Greece and the entire Mediterranean worked in the Library of Alexandria. One of them was the ancient Greek astronomer Eratosthenes.

While living in Alexandria, Eratosthenes received amazing letters from the city of Siena in Egypt. There, in particular, it was said that on the day of the summer solstice:

The shadow of a man looking into a deep well will cover the reflection of the Sun at noon.

In other words, the Sun will be directly overhead, not deviating a single degree to the south, north, east or west. And if you had a completely vertical object, it wouldn't cast shadows.

But Eratosthenes knew that this was not the case in Alexandria. The sun approaches its highest point at noon during the summer solstice in Alexandria closer than on other days, but vertical objects there also cast a shadow.

And like any good scientist, Eratosthenes set up an experiment. By measuring the length of the shadow cast by a vertical stick on the day of the summer solstice, he was able to measure the angle between the Sun and the vertical direction in Alexandria.

He got one fiftieth of a circle, or 7.2 degrees. But at the same time in Siena, the angle between the Sun and the vertical stick was zero degrees! Why could this happen? Perhaps, thanks to a brilliant insight, Eratosthenes realized that the Sun's rays can be parallel, and the Earth can be curved!

If then he could find out the distance from Alexandria to Syene, knowing the difference in angles, he could calculate the circumference of the Earth! If Eratosthenes were the supervisor of a graduate student, he would have sent him on his way to measure the distance!

But instead he had to rely on the then known distance between the two cities. And the most accurate method of measurement then was ...

Camel travel. One can understand the criticism of such accuracy. And yet, he considered the distance between Syene and Alexandria to be 5,000 stadia. The only question is the length of the stage. The answer depends on whether Eratosthenes, a Greek who lived in Egypt, used the Attic or Egyptian stages, which historians are still arguing about. The Attic stadia was used more often and is 185 meters long. Using this value, you can get the circumference of the Earth equal to 46,620 km, which is 16% more than the real value.

But the Egyptian stadia is only 157.5 meters, and perhaps this is what Eratosthenes had in mind. In this case, you get 39,375, which is different from contemporary meaning at 40,041 km by only 2%!

Regardless of the numbers, Eratosthenes became the world's first geographer, invented the concepts of latitude and longitude used to this day, and built the first models and maps based on a spherical Earth.

And although much has been lost over the millennia that have passed since then, the ideas of a spherical Earth and knowledge of its approximate circumference have not disappeared. Today, anyone can repeat the same experiment with two places at the same longitude, and by measuring the lengths of the shadows, get the circumference of the Earth! Not bad, considering that the first direct photographic proof of the Earth's curvature would not come until 1946!

By knowing the shape and size of the Earth, as early as 240 BC, we have been able to figure out a lot of wonderful things, including the size and distance of the Moon! Therefore, we give credit to Eratosthenes for discovering that the Earth is round and for the first accurate calculation of its size!

If there is one thing that Columbus should be remembered for in relation to the size and shape of the Earth, it is for using too small values for its circumference! His estimates of the distances by which he convinced that a ship could pass from Europe directly to India (if the Americas did not exist) were incredibly small! And if there were no Americas, they and the team would die of starvation before reaching Asia!

For me, the fact that our planet is round is obvious almost from kindergarten age. And therefore, as soon as I read about the fact that another “wise man” convinces us that the Earth is flat, I want to bang my head against the wall. Aristotle so many years ago was able to find evidence of the sphericity of the planet and some in the 21st century can't even bother to read them!

Before Aristotle

Ancient people didn't believe in anything! Who believed that the planet standing on whales who thought that turtles and elephants are involved in the device of the world. They were clearly better with fantasy than with scientific knowledge.

But the general idea was that whatever the Earth stood on, it was flat. But little by little, these ideas began to change.

It all started before Aristotle. He assumed that the planet has the shape of a ball, Pythagoras.

He built his idea on the following reasoning:

Everything in the world strives for harmony in your device.
Earth– is also no exception. So she too should be the most correct form.
BUT the most correct form According to Pythagoras, - ball. This means that the Earth is also a sphere, everything is logical.

Of course, no one was convinced by this argument. And then he got down to business. Aristotle, who proposed much more compelling arguments.

Aristotle and his evidence

First proof related with ships sailing from the sea. If you observe them, a strange optical effect is noticeable: first noticeably the approach of the masts and then everything else.

But if the boat was floating on a plane, such a phenomenon would not arise. Its entire front should have come into view at once.

Second proof– observable lunar eclipses. On our satellite on certain days you can see a shadow that makes the moon less bright. If you look closely, it is noticeable that this shadow is round. And since our planet leaves it, then the Earth itself must also have such a shape.

But here one could say that the Earth is not a sphere, but simply a round disk. refutes this assumption. the third proof is the stars. At different ends of the planet will be visible different parts of the starry sky which confirms: Earth simply obliged have a spherical shape.