How did the ancients use standard watches to measure time?
In ancient times, people worked at sunrise and rested at sunset. From the day when the sun rises and sets regularly, they intuitively felt the relationship between the sun and time, and began to determine the time through the position of the sun in the sky. But it's hard to be precise.
According to records, more than 3000 years ago, Zhou Gongdan, the prime minister of the Western Zhou Dynasty, set up an instrument in Dengfeng County, Henan Province to determine the time by measuring the length of the sun shadow, which was called the "standard watch". This should be the earliest timer in the world.
Gauge consists of gauge and gauge: gauge is a flat scale, and gauge is an upright benchmark, which is placed at both ends of gauge and perpendicular to gauge.
Most GUIs are made of stone or copper, with shaded scales, and then a watch at one end becomes a standard watch. A watch is an upright pole. When the sun shines on it, it will cast a shadow. According to the shadow and direction and length, the time can be read.
Using the length of the sun shadow measured by the standard table, we can determine several larger solar terms, such as the short shadow from summer to the sun and the long shadow from winter to the sun. In a day, according to the change of shadow length, we can also know the approximate time.
When the sun returns to the north and south poles, its distance from the celestial pole determines the length of the surface shadow on the ground. It is difficult to measure the distance from the sun to the celestial pole directly, and only by measuring the shadow of the sun can we know it indirectly. The purpose of measuring shadows with standard meters is to infer the position of the sun in the sky.
It is easy to measure the sun shadow with a standard meter. Our country is located in the northern hemisphere. When measuring, the gauge rod faces south, so that its axis is placed on the flat ground illuminated by solar energy along the meridian and fixed.
At noon every day, when the sun shadow caused by the viewing pole coincides with the central axis of the ruler, the length of the sun shadow of the day is recorded in words or the trajectory point of the vertex of the sun shadow of the day is directly drawn on the ruler to complete the sun shadow measurement of the day.
Measuring the shadow of the sun with a standard meter is a meticulous work that takes a whole year as a cycle, and it must be done patiently, otherwise it will come to nothing. Especially the winter solstice, summer solstice, vernal equinox and autumn equinox are particularly critical. As long as the shadow length with extreme significance is measured, the length of the tropic year can be directly determined.
Due to the influence of climate and the fact that the winter solstice does not necessarily occur at noon, the measured results are often different from the actual situation. People measured for several years in a row, and then took the longest year as the solstice moment at noon in winter.
Obviously, this method has some human factors, and it is not necessarily consistent with the actual time of winter solstice.
Zu Chongzhi has found a solution to this problem. He used the viewpoint of symmetry to measure the length of the sun shadow in the days before the winter solstice and in the days after the winter solstice, and calculated the exact time of the winter solstice.
Compared with traditional methods, Zu Chongzhi's method has obvious advantages. First of all, it is not affected by the climate, as long as it is measured in the days around the winter solstice.
Secondly, the accuracy is improved. Because the length of the solar shadow changes slowly around the winter solstice, Zu Chongzhi chose the solstice of more than 20 days around the winter solstice for observation. At this time, the sun shadow changes obviously, and the measurement and calculation are relatively easy.
More importantly, this method can accurately measure the winter solstice time, because the winter solstice time is not exactly at noon, but it can be calculated by this method.
According to Zu Chongzhi's calculation, the length of a tropical year is 365.2428 days. This data is very accurate, and it was not until more than 700 years later that a more accurate julian calendar appeared.
In Europe, julian calendar has been implemented until16th century, and its tropical year is 365.25, which is obviously not as good as that of Zu Chongzhi.
Zu Chongzhi skillfully measured the shadow of the sun and obtained relatively accurate data. It is of great practical significance to make a legislative calculation of him and compile Da Li Ming.
Although Zu Chongzhi's calculation method is not perfect, his invention is a milestone in measuring the development of winter solstice time in ancient China, which is respected by later astronomers and taken for granted.
After Zu Chongzhi, many people improved the method of measuring solar shadow, the most famous of which was the improvement of measuring tools by astronomer Guo Shoujing in Yuan Dynasty.
Guo Shoujing thinks that the reading accuracy of traditional photogrammetry methods is too low, because the units of minutes, millimeters, millimeters and seconds are too small to be distinguished by naked eyes. In order to keep the measured value unchanged, it is necessary to increase the height of the workbench by a corresponding multiple. Therefore, it is necessary to build a high table.
Guo Shoujing's high watches are very fine in workmanship, which is five times that of traditional watches. However, with the increase of tables, the clarity of images will inevitably decrease. In this case, Guo Shoujing developed a measuring tool called Seisuke, which completely solved this problem.
Guo Shoujing made outstanding achievements in these two aspects by building high tables and making landscape symbols, which greatly facilitated people's solar shadow measurement and made indelible contributions to the development of ancient astronomy and surveying in China.