What kind of tool was it in ancient times?

The sundial, also known as the sundial, is an ancient time measuring instrument in China, which uses the shadow of the sun to measure time.

A sundial usually consists of a copper pointer and a stone disk. The copper pointer is called "pointer", which passes through the center of the disk vertically and acts as a neutral rod in the standard table. Therefore, the needle is also called "table"; The stone plate is called Mian and placed on the stone platform.

The south is high and the north is low, so that the coffin surface is parallel to the equatorial plane, and the upper end of the coffin needle points to the north celestial pole and the lower end points to the south celestial pole. There are scales on both sides of the coffin. Molecules, Ugliness, Yin, Mao, Chen, Si, Wu, Wei, Shen, You, Xu and Hai have twelve hours, and each hour is divided into "the beginning of the time" and "the right time", and a day is exactly 24 hours.

Most sundials show apparent solar time, and the design of some of them has been changed to show standard time or daylight saving time. The sundial can display not only the time of day, but also the solar terms and months. Of course, its shortcomings are also obvious. It is huge and cannot be used when there is no sunshine, such as cloudy days and cloudy nights.

How does it work over time:

1. During the day, the shadows cast by objects illuminated by the sun are constantly changing.

2. First, the length of the shadow is changing. The shadow is the longest in the morning. As time goes on, the shadow becomes shorter and shorter after noon.

Second, the direction of the shadow is changing. North of the Tropic of Cancer, the shadow in the morning is in the west, the shadow at noon is in the north, and the shadow at night is in the east. In principle, it can be timed according to the length or direction of the shadow, but it is more convenient to time according to the direction of the shadow.

4. Therefore, timing is usually based on the position of the shadow. As time goes on, the shadow on the needle slowly moves from west to east. The moving shadow of the hand seems to be the pointer of a modern clock, while the surface of the hand is the surface of the clock to show the time.

5. In the morning, the shadow is cast near Shi Mao at the western end of the disc; When the sun reaches the highest position due south (upper meridian), the needle shadow is located due north (lower), indicating the local noon time. In the afternoon, the sun moves west and the shadow leans east, pointing to each hour in turn.