Can you judge the time according to the length of the shadow?

You can judge the time by the length of the shadow, but you need to use the sundial.

Modern "sundial" refers to a kind of timing instrument used by ancient humans to measure time, also known as "sundial". Its principle is to use the projection direction of the sun to measure and divide the time, which usually consists of a pointer (watch) and a surface (scale watch seat).

The sundial timing method is a great invention in the field of astronomical timing, which has been used by human beings for thousands of years.

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.

Extended data

principle of operation

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

1, the length of the shadow is changing. The shadow is the longest in the morning. As time goes on, the shadow becomes shorter and longer after noon. 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. Therefore, the timing is usually based on the position of the shadow.

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.

Reference source: Baidu Encyclopedia-sundial