What does sun clock think of time?

In the long river of history, astronomy and timing have developed together. It can be said that with astronomy, there is time. Timekeeping instruments, like astronomical instruments, are gradually improved after a long development process.

The oldest timekeeping instruments are earth gauges, gauges and sundials, whose principle is to time by the projection and orientation of the sun, commonly known as sun clock.

sundial

The sundial, also known as the sundial instrument, is also an instrument for observing the time of the sun shadow. The difference between it and a standard watch is that the standard watch determines the season, the number of days in the whole year, the winter solstice and the summer solstice, and calculates the calendar according to the length of the sun shadow. The application of sundials is mainly to specify the time or the number of minutes at that time according to the position of the sun's shadow. It is a kind of timing instrument commonly used in ancient China, but it is rarely recorded in history books. At present, the earliest record in historical materials is the section of "History of Han Dynasty, Chronology of Han Dynasty, Making the Calendar of Han Dynasty": "Taishiling" Sima Qian put forward that "it is to decide the event, master the instrument and make the next one."

Sui Shu Tian Wen Zhi recorded Geng Xu's achievements. "Observing the leakage of the sundial is the foundation of measuring the image of heaven and earth." The history of tomorrow records the shape and timing of the sundial in detail. Compared with the standard meter, it is much more complicated and can be said to be a real instrument. In the Qing dynasty, it not only developed.

The name of a sundial consists of two words: the sun and the sundial. The sun refers to the sun, the sundial refers to the shadow and the sundial refers to the shadow of the sun. So the so-called sundial is to determine the time by measuring the shadow of the sun during the day. The second is that the direction of the shadow is changing, because we are in the northern hemisphere, 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, we can time according to the length or direction of the shadow, but it is more convenient to time according to the direction of the shadow. So sundials are usually timed according to the direction of shadows. Because it must rely on sunlight, it can't be used on cloudy days and cloudy nights. Therefore, it is only used for sundials.

sundial

According to records, in the Spring and Autumn Period, a kind of clock named "Gui" appeared in China.

It consists of a ruler "reed" placed horizontally in the north-south direction and a benchmark "table" erected on the plane.

By measuring the length of the shadow, we can determine the noon time and calculate 24 solar terms. From the periodic change of shadow length, such as the time interval between the longest and shortest shadows in two consecutive days, the length (including days) of a tropical year can be determined. At the same time, we can also measure that the shortest shadow day is the summer solstice and the longest shadow day is the winter solstice.

The disadvantage of standard meter is that its timing accuracy is not high, and its application is limited, so it is impossible to measure time at night and on cloudy days.

Dengfeng Observatory is the earliest existing observatory in China, which consists of the observatory itself and the Shi Gui. It has been more than 700 years since Guo Shoujing, an outstanding scientist in Yuan Dynasty, was built as the national observation center at that time. Guo Shoujing used this observatory to compile the most advanced calendar at that time? The calendar has been implemented for 360 years, and the length of a tropical year is calculated, which is only 26 seconds shorter than the actual time for the earth to go around the sun. The present solar calendar of the world was made in A.D. 1582, which is consistent with the timing calendar of China, but 300 years later. Dengfeng Observatory has attracted worldwide attention. Observatory, Timekeeping Calendar and Guo Shoujing.