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# What size does the circumference of the Earth have?

The earth is round - this is well known. And what else do we know about its shape and size? Who among us will recall as a memory how many kilometers the Earth's circumference contains along the equator? And on the meridian? Who knows, when and how was the length of the earth's circumference measured for the first time? Meanwhile, these facts are extremely interesting.

The Earth's circumference was measured for the first timeAncient Greek mathematician named Eratosthenes, who lived in the city of Siena. At that time, scientists already knew that the Earth in form is a ball. Observing the heavenly light at different times of the day, Eratosthenes noticed that at the same time, the sun, being observed from Siena, is located exactly at the zenith, while in Alexandria, on the same day and hour, it deviates to a certain angle.

Observations were conducted annually on the day of the summer solstice. Measuring this angle with the help of astronomical instruments, the scientist established that it is 1/50 of the total circumference.

As is known, the total circle is 360degrees. Thus, it suffices to know the chord of an angle of 1 degree (that is, the distance between points on the surface of the Earth lying on the rays with an angular distance between them of 1 degree). Then the resulting value should be multiplied by 360.

Taking the distance between cities by the length of the chordAlexandria and Siena (5 thousand Egyptian stages) and assuming that these cities are on the same meridian, Eratosthenes made the necessary calculations and named a figure that equaled the circumference of the Earth - 252 thousand Egyptian stages.

For that time, this measurement was enoughaccurate, because reliable methods for measuring the distance between cities did not exist, and the path from Siena to Alexandria was measured by the speed of the camel caravan.

Subsequently, scientists from different countries repeatedlymeasured and refined the value, which is the length of the circumference of the Earth. In the 17th century, a Dutch scientist named Sibelius came up with a way to measure distances with the help of the first theodolites - special geodetic instruments. This method was called triangulation and is based on the construction of a large number of triangles with the measurement of the basis of each of them.

The method of triangulation is still used today, the entire earth's surface is virtually divided and delineated into large triangles.

Russian scientists also contributed to these studies. In the 19th century, the Earth's circumference was measured at the Pulkovo Observatory, led by V. Ya. Struve.

Until the middle of the 17th century, the Earth was considered a spherecorrect form. But later, some facts were accumulated, indicating a decrease in the force of gravity from the equator to the pole. Scientists fiercely discussed the causes of this, the most plausible was the theory of the Earth's compression from the poles.

To test this hypothesis by the French AcademyTwo independent expeditions (in 1735 and 1736) were organized, which measured the length of the equatorial and polar degrees, respectively, in Peru and in Lapland. At the equator, the degree, as it turned out, is shorter!

Subsequently, other, more accurate measurements confirmed that the polar circle of the Earth is shorter than the equatorial one at 21.4 km.

At present, high-precisionMeasurements using the latest research methods and modern instruments. In our country, officially approved data obtained by Soviet scientists Izotov AA and Krasovsky FN According to these studies, the circumference of our planet along the equator is 40075.7 kilometers, along the meridian - 40008.55 km. The equatorial radius of the globe (the so-called semi-major axis) is 6,378,245 meters, the polar axis (small semiaxis) is 6,356,863 meters.

The area of ​​the earth's surface is 510 million square meters. kilometers, of which only 29% belong. The volume of the earth's "ball" is 1083 billion cubic meters. kilometers. The mass of our planet is characterized by the figure 6X10 ^ 21 tons. About 7% of them are water resources.

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