The earth is round - it is well known. And what else do we know about its shape and size? How many of us will recall from memory how many kilometers the circumference of the Earth contains along the equator? And on the meridian? Who knows when and how the circumference of the earth was first measured? Meanwhile, these facts are extremely interesting.
For the first time, the circumference of the Earth was measured by an ancient Greek mathematician named Eratosthenes, who lived in the city of Siena. At that time, scientists already knew that the Earth was a ball in shape. Watching the celestial luminary at different times of the day, Eratosthenes noticed that at the same time, the sun, being observed from Siena, is located exactly at its zenith, while in Alexandria on the same day and hour it deviates to a certain angle.
Observations were carried out annually on the summer solstice. By measuring this angle using astronomical instruments, the scientist found that it is 1/50 of the full circle.
As you know, the full circle is 360 degrees. Thus, it is enough to know the chord of an angle of 1 degree (i.e., 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 the cities of Alexandria and Siena (5 thousand Egyptian stages) for the length of the chord and assuming that these cities lie on the same meridian, Eratosthenes made the necessary calculations and named the figure that equaled the circumference of the Earth - 252 thousand Egyptian stages.
For that time, this measurement was quite accurate, because there were no reliable methods for measuring the distance between cities, and the path from Siena to Alexandria was measured by the speed of the caravan of camels.
Subsequently, scientists from different countries repeatedly measured and clarified the value of the circumference of the Earth. In the 17th century, a Dutch scientist by the name of Sibelius came up with a way to measure distances using the first theodolites - special geodetic instruments. This method was called triangulation and is based on the construction of a large number of triangles with a 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 laid out into large triangles.
Russian scientists also contributed to these studies. In the 19th century, the circumference of the Earth was measured at the Pulkovo Observatory, led the research of V. Ya. Struve.
Until the mid-17th century, the Earth was considered a ball of regular shape. But later some facts were accumulated, indicating a decrease in the force of gravity from the equator to the pole. Scientists fiercely debated about the reasons for this, the most plausible theory was the compression of the Earth from the poles.
To test this hypothesis, the French Academy organized two independent expeditions (in 1735 and 1736), which measured the lengths of the equatorial and polar degrees in Peru and Lapland, respectively. At the equator, the degree, as it turned out, is shorter!
Subsequently, other, more accurate measurements confirmed that the Earth’s polar circle is 21.4 km shorter than the equatorial.
Currently, high-precision measurements have been made using the latest research methods and modern instruments. According to these studies, the circumference of our planet along the equator is 40,075.7 kilometers, along the meridian - 4,0008.55 km. The equatorial radius of the globe (the so-called major semi-axis) is 6378245 meters, the polar (minor semi-axis) - 6356863 meters.
The surface area of the earth is 510 million square meters. kilometers, of which only 29% belong to land. The volume of the earth "ball" - 1083 billion cubic meters. kilometers. The mass of our planet is characterized by the figure 6X10 ^ 21 tons. Of these, about 7% are water resources.