How is the gauge measured?

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.