Find two places far apart on the earth (for example, hundreds of kilometers apart) and measure the angle between sunlight and the ground at the same time. Assuming that sunlight is parallel light, the central angles of two places on the earth can be calculated. The distance between two places divided by the central angle (radian) is radius of the earth.
In order to simplify the calculation, it is usually measured when the sun hits the earth directly, so the central angle is the complementary angle between the sun and the ground at another place, so the ancient Greeks measured the radius of the earth.
The radius of the earth is calculated by measuring the circumference of the earth.
Scientists calculate the radius of the earth by measuring its circumference. The circumference of the earth refers to the distance required to make a circle along the equatorial line of the earth, which can be obtained by satellite measurement and other methods. The radius of the earth's pole refers to the length of a line segment perpendicular to the equatorial line of the earth, which can be obtained by astronomical observation and other methods. From these two data, we can calculate the average radius of the earth.
Radius of the earth's survey is a long historical process. As early as ancient times, people began to try to measure the size of the earth. In the 3rd century BC, the Greek mathematician Eratosthenes estimated the size of the earth by observing its shape and the length of its shadow. With the continuous progress of science and technology, the method of measuring radius of the earth is more and more accurate.
Radius of the earth survey is very important for earth science research and space technology application. Radius of the earth's measurement is not only related to the shape and size of the earth, but also to its mass, density and gravitational field. In the application of aviation, navigation, communication and meteorology, the accurate measurement of radius of the earth also plays a vital role.
Evolution of the shape and size of the earth;
1. As early as the third century BC, the famous Greek mathematician Eratosthenes tried to estimate the size of the earth. He used the length of the sun shadow from summer solstice as reference data, and calculated the size of the earth by measuring the difference of the length of the sun shadow in different places. Although this method is not very accurate, it provides valuable reference for later scientists.
2. In modern times, people began to adopt more accurate and comprehensive measurement methods. For example, in the18th century, the Royal Society launched a large-scale scientific expedition called "Bird Exploration". Through long-term measurement and calculation, scientists have found that the average radius of the earth is about 637 1km. This result became the most authoritative measurement data of radius of the earth at that time.
3. With the continuous progress of science and technology, the measurement methods of the shape and size of the earth are also improving. For example, the commonly used satellite remote sensing and rubber ant laser ranging technology can accurately measure the shape and size of the earth, not only get the average radius of the earth, but also calculate the gravity field, deformation, seismic activity and other parameters of the earth.