The times when the Earth was considered a plane have long ago become a thing of the past. Today even children know that the planet is a ball.
But if the Earth is spherical, then you can determine its diameter.
The question of the diameter of the globe is not as simple asCan seem at first glance, because the very concept of "the globe" is very conditional. In a real ball, the diameter will always be the same, no matter where the segment that connects two points on the surface of the sphere and passes through the center is drawn.
In the case of the Earth, this does not appearPossible, because its sphericity is far from ideal (in nature there are no ideal geometric figures and bodies, they are abstract geometric concepts). For an exact designation of the Earth scientists even had to introduce a special concept - "geoid."
Official diameter of the Earth
The magnitude of the diameter of the Earth is determined by theHis place will be measured. For convenience, two parameters are accepted for the officially recognized diameter: the diameter of the Earth along the equator and the distance between the North and South poles. The first figure is 12 756.274 km, and the second - 12 714, the difference between them is a little less than 43 km.
These numbers do not make much impression,They are inferior even to the distance between Moscow and Krasnodar - two cities located in the territory of one country. Nevertheless, it was not easy to calculate them.
Calculating the diameter of the Earth
The diameter of the planet is calculated by the same geometric formula as any other diameter.
To find the perimeter of a circle,Multiply its diameter by the number? And. Therefore, to find the diameter of the Earth, you need to measure its circumference in the corresponding section (along the equator or in the plane of the poles) and divide it by the number?
The first person who tried to measureThe circumference of the Earth, was the ancient Greek scientist Eratosthenes of Cyrene. He noticed that in the Siena (nowadays - Aswan) on the day of the summer solstice, the Sun is at its zenith, illuminating the bottom of a deep well. In Alexandria, on the same day, it was defended from the zenith by 1/50 of a circle. From this scientist concluded that the distance from Alexandria to Siena is 1/50 of the circumference of the Earth. The distance between these cities is 5 000 Greek stages (about 787.5 km), therefore, the circumference of the Earth is 250 000 stages (about 39 375 km).
At the disposal of modern scientists there are morePerfect means of measurement, but their theoretical basis corresponds to the idea of Eratosthenes. At two points, located several hundred kilometers from each other, fix the position of the Sun or certain stars in the sky and calculate the difference between the results of two measurements in degrees. Knowing the distance in kilometers, it's easy to calculate the length of one degree, and then multiply it by 360.
To clarify the size of the Earth, both laser ranging equipment and satellite surveillance systems are used.
To date, it is believed that the Earth's circumference along the equator is 40,075.017 km, and along the meridian - 40,007.86. Eratosthenes was only a little mistaken.
The magnitude of both the circle and the diameter of the Earth increases because of the meteorite substance that constantly falls on the Earth, but this process is very slow.