Earth is round - this is common knowledge.What we do know about her shape and size?Who among us would call to mind how many kilometers contains the Earth's circumference at the equator?And along the meridian?Who know how and when was the first time measured the length of the circumference of the Earth?Meanwhile, these facts are extremely interesting.
first circumference of the Earth has been measured by the ancient Greek mathematician named Eratosthenes, who lived in the city of Siena.While scientists already knew that the earth is shaped balloon.Watching the heavenly body at different times of the day, Eratosthenes noticed that in one and the same time, the sun, as observed from Siena, is located exactly at the zenith, while in Alexandria on the same day and the hour is deflected by a certain angle.
observations were made annually on the summer solstice.By measuring the angle with the help of astronomical instruments, scientists have found that it is 1/50 of the full circle.
As you know, full circle equals 360 degrees.Thus, it suffices to know the chord angle of 1 degree (t. E. The distance between two points on the Earth's surface, lying on the rays with an angular spacing of 1 degree).The resulting value should be multiplied by 360.
Taking the chord length distance between the city of Alexandria and Siena (5000 Egyptian stages), and assuming that these cities are on the same meridian, Eratosthenes made the necessary calculations and named a figure that equals the circumference of the Earth -252 thousand Egyptian stages.
For that time it was quite accurate measurement, because reliable methods of measuring the distance between the cities did not exist, and the road from Siena to Alexandria measure the speed of a caravan of camels.
Subsequently, scientists from different countries repeatedly measured and specifies the value that is the circumference of the Earth.In the 17th century Dutch scientist by the name of Sibelius came up with a way to measure distances using the first theodolites - Special surveying instruments.This method has been called triangulation and based on the construction of a large number of triangles with the measurement of the basis of each of them.
method of triangulation is used to this day, the entire surface of the earth virtually divided and lined by long triangles.
Russian scientists have also contributed to this research.In the 19th century the Earth's circumference was measured at the Pulkovo Observatory, he led the research Struve.
Until the mid 17th century the Earth was considered the correct form a ball.But later we accumulated some evidence to reduce the forces of gravity from the equator to the pole.Scientists have fiercely debated the reasons for this, the most plausible theory has been recognized by the compression of the Earth at the poles.
To test this hypothesis, the French Academy organized two independent expedition (in 1735 and 1736 respectively), which measured the length of the equatorial and polar degrees, respectively, in Peru, and Lapland.At the equator, degrees, as it turned out, in short!
Subsequently, other more precise measurements have confirmed that the polar equatorial circumference of the Earth is shorter at 21.4 km.
Currently produced high-precision measurements using the latest research methods and modern instruments.In our country, approved the data obtained by Soviet scientists AA Izotov and Krasovsky FN According to these studies, the circumference of the planet's equator - 40,075.7 kilometers, along the meridian - 40008.55 km.The equatorial radius of the earth (ie. N. Semi-major axis) is equal to 6,378,245 meters, polar (minor axis) - 6,356,863 meters.
area of the earth's surface - 510 million square meters.kilometers of land which belongs to only 29%.The volume of the earth "ball" - 1.083 trillion cubic meters.kilometers.The weight of the world is characterized by the number 6x10 ^ 21 tons.Of these, about 7% falls on the share of water resources.
