It is now every schoolchild knows that the planet is round, which is all of us the force of gravity, which does not allow us to fall down and fly out of the atmosphere... But in the beginning of our era, this view is not shared by all. In the III century, the famous writer and philosopher Lachance wrote: "Is there some whimsical dreamer who would imagine that there are people walking upside down and upside down? All that we on this side lies down there hanging? That the grass and trees grow there, falling down, and hail there falls from the bottom up?" He was supported by Cozma and Indicplus in his book "Christian topography" and even illustrated his "compelling" evidence ironic picture with four figures.
However, the hypothesis that our planet has the shape of a ball, there was a very long time. First this idea expressed in the VI century BC Greek philosopher and mathematician Pythagoras. Another philosopher, Aristotle, who lived in Ancient Greece, two centuries later, led evidence of sphericity: indeed, during lunar eclipses, the Earth casts on the moon the shadow of it is round shape!
Gradually the idea that the Earth is a ball hanging in space and has no resting, spread widely. Over the centuries, people have long known that the Earth is not flat and is not resting on the whales or elephants... We walked around light, crossed our ball literally in all directions, and I flew it on the plane, photographed from space. We even know, why not just ours, but all the other planets and the Sun and stars, and Moon, and other large satellites it is "round"and not some other form. Because they are large, have a huge mass. Their own gravitational force - gravity - tends to give heavenly bodies in the shape of a ball.
If even appeared certain force greater than gravity, which would give the Land of the form, say, suitcases, it would still the same: as soon as the action of this force is stopped, the force of gravitation would start again to collect the Earth into a ball, "pulling" protruding parts until all points of the surface would not be at equal distance from the center.
Not a ball!
In the XVII century, the famous physicist and mathematician Newton, made a bold assumption that the Earth is not a ball, or rather, not exactly a ball. Suggested - and it is mathematically proved.
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" with water. Calculations showed that the water was set at different levels. Because of the polar pit water is only effective gravitational force, and in the Equatorial she still opposes the centrifugal force. The scientist claimed that both the water column provided at the center of the Earth the same pressure, that is, that they have equal weight, the water level in the Equatorial well should be higher according to Newton on 1/230 of the average radius of the planet. In other words, the distance from the center to the equator more than to the pole.
To verify the calculations of Newton, the Paris Academy of Sciences sent in 1735 - 1737 two expeditions in Peru and Lapland. The members of the expedition were to measure an arc of Meridian - 1 degrees each, one in the Equatorial latitudes, in Peru, the other in the Arctic, in Feet land. After data processing expeditions, head North, surveyor Pierre-Louis Maupertuis, announced that Newton rights: the Earth is compressed at the poles! This discovery Maupertuis immortalized Voltaire... the epigram:
The messenger of physics, the brave sailor,
Overcoming mountains and the sea.
Downhill carrying quadrant amid the snow and swamps,
Almost turned into Lopera.
Learned you after many losses.
He knew Newton, not going out the door.
In vain Voltaire was so sarcastic: how science can exist without experimental evidence theories?!
Anyway, now we know that the Earth is flattened near the poles (if anything - stretched near the equator). Overall, however, quite a bit: the polar radius is 6357 km and the Equatorial - 6378 km, just 21 km more.
Similar to a pear?
But can we call Earth, let not the ball, but spljusnutymi" ball, namely the ellipsoid of rotation? Because, as we know, the relief in her uneven: there are mountains, there is depression. In addition, it is acted by the force of attraction of other celestial bodies first the sun and the moon. May their influence is not great, but still the Moon is capable of several meters to distort the form of a liquid shell of the Earth - the oceans, creating the tides. Means in different points of the radii of the "rotation" different!
In addition to the North is a liquid ocean, and on the South - solid, the continent is covered with ice - Antarctica. It turns out that the Earth is not quite the right shape resembles a pear, elongated to the North pole. But by and large, its surface is so complex that it is not amenable to a rigorous mathematical description. Therefore, the shape of the Earth, scientists have proposed a special name - the geoid. The geoid is irregular stereometric figure. Its surface is approximately equal to the surface of the World ocean and continues on the mainland. The same "altitude", which indicate the atlases and dictionaries, is measured directly from the surface of the geoid.
The geoid is not a geoid!
To be quite honest, I have to admit that due to differences in temperature in different parts of the world and the salinity of the oceans and seas, atmospheric pressure and other factors surface water surface does not coincide in form with the geoid, and has deviations. For example, at the latitude of the Panama canal the level difference of the Pacific and Atlantic oceans is 62 see
On the shape of the globe impact of a strong earthquake. One of such magnitude 9 earthquakes occurred on 26 December 2004 in Southeast Asia, Sumatra. Professor at the University of Milan Roberto Sabadini and Giorgio dalla vía believe that it left a "scar" on the gravitational field of the planet, resulting in the geoid significantly impacted. To verify this assumption, the Europeans intend to send into orbit a new satellite GOCE, equipped with highly sensitive equipment. I hope that soon he will send us accurate information about what form has the Earth today.