Earth is the only known planet in the universe on which life exists. Its age is estimated from about 3.5-4.5 billion years.
For many millennia, man has represented the earth as a plane mounted on a support. And such a view has existed for many centuries and among different peoples of the world. But navigation, long military campaigns, and trade expeditions provided food for thought to an inquiring mind.
For the first time, the ancient Greek scientists expressed their assumptions about the Earth as a ball. In the 3rd century BC (235 BC) Erastofen, (geographer and astronomer) determined the diameter of the planet Earth from the Sun at a certain point located near the city of Alexandria. This city is the center of science and culture of Ancient Egypt. Archaeological materials, studies of modern Egyptologists indicate that already in the 3rd millennium BC the Egyptians had a very good idea of the universe and of the earth.
On the day of the summer solstice (according to the modern calendar June 22), Erastofen calculated the angle of incidence of sunlight and the shadow of the obelisk. The data obtained allowed him to determine the radius of the Earth. In the 2nd century BC Ptolemy tried to calculate the circumference of the planet in a similar way.
Ancient astronomers proceeded from the postulates of geocentric theory - all visible celestial bodies move around the Earth. In the Middle Ages (9-11 centuries), Central Asian scholars also conducted measuring studies. They analyzed the works of ancient scholars. The diameter of the Earth was calculated by Indian scientists. The studies were carried out in different ways, at different points on the globe and in different units of measurement. Nevertheless, the results of calculations of the parameters of our planet, the Sun, the Moon were close in value.
In the 16th century, the position of supporters of the heliocentric structure of the Universe was strengthened. The sun is the center around which planets revolve, among which our Earth is far from the largest.
The interaction of our planet with the Sun, Moon and other planets of the universe is undeniable. It is assumed that the Earth and the Moon once formed a single whole. But, faced with a huge asteroid billions of years ago, the Moon became a separate cosmic body. Its revolution around our planet is 27 days and almost 7 hours - this is our earthly month. And the time for which the Earth wraps around the Sun - 365 days - the earth's year.
Naturally, there were also errors in the centuries-old measurements of the parameters of our planet; today the following dimensions have been officially recognized: the radius of the Earth - 6378.1363 km; Earth diameter at the equator - 12756, 274 km; diameter from the South to the North Pole - 12,514 km.
Actually, speaking about the parameters of the planet, it is more logical to talk about its diameters, since the Earth is not an ideal ball, the strength of rotation makes it an ellipse or geoid. It is easy to calculate that the difference between the values is 43 km, and the average diameter of the Earth is 12743.2 km.
How accurate are these numbers? Measurements and refinement of the Earth's parameters are ongoing. Modern scientists work in international teams, which allows you to receive information from different parts of the globe. In 2007, the results of measurements were published, which showed that, compared with 2000, the diameter of the Earth decreased by 5 millimeters. Does this mean that our planet is shrinking? Rather, it is evidence that measurement methods are being improved, more complete and accurate information, modern geophysical models are used.
Thus, the average diameter of the Earth according to the latest updated data is 12,756.274 km.
In modern research, three main methods are used:
- Measurement of radio waves (quasars) that receive 70 radio telescopes located at different points on our planet.
- Satellite laser ranging, when the distance from the spacecraft to the surface of the earth is measured by a laser.
- Research programs for GPS and DORIS satellite systems.