Measuring the Earth

Eratosthenes calculated the circumference of the Earth through shadows, Hipparchus used solar eclipses to calculate the distance between the Earth and the Moon, Bode calculated the distance between the Earth and the Sun through the transit of Venus, and in the Book of Rites, he estimated the size of the Sun using a bamboo pole. In the era without satellites, astronomers relied on their intelligence and mathematical methods to complete one seemingly impossible celestial measurement after another.

The unit is designed for unsupervised public use: controls are recessed or shielded, moving parts are enclosed, and the interface is operable by a child of about six with no instruction. Where a screen is used, the language can be switched without changing the hardware, and the content can be replaced on site.

Eratosthenes was a knowledgeable Greek scholar and the first person in the world to measure the circumference of the Earth. How did he do it at that time? At that time, Saini, located on the banks of the Nile River, was 800 kilometers south of Alexandria and happened to be on the Tropic of Cancer. At noon on the summer solstice every year, the sun is located at the zenith of Saini, and the sunlight can vertically shine on the bottom of the local well. At the same time, the northern city of Alexandria is different. The spires there will have the shadow of a stone monument due to the different angles of the sun. After measuring the length of the shadow and the height of the spire, the angle between the upright square spire and the solar ray is calculated to be 7.2 °. According to mathematical laws, when a ray passes through two parallel lines, their diagonals are equal. Therefore, the angle between the two places on the circumference of the Earth is also 7.2 °. Because this value is exactly 1/50 of the circumference, the circumference of the Earth is two.