What did the ancients use to determine the 24 solar terms?

In ancient times, there were probably several methods of division:

1. One way is to watch the Big Dipper at dusk shortly after dark and set the solar terms by pointing to bucket handle. The handle of the barrel points to the east, the vernal equinox, the south, the summer solstice, the west, the autumn equinox and the north, and the winter solstice.

2. There is also a painting method, that is, at dusk, look at what constellation the zenith is, such as the star at the zenith at dusk, which is called "fire" in ancient books, that is, "Antares", that is, summer has arrived; In addition, if the constellation you see at dusk is the Pleiades, which is now the Pleiades cluster of Taurus in astronomy, it is the winter solstice.

3. The third drawing method is to measure the shadow of the sun with a soil gauge, that is, stand on a pole and see the length of the shadow at noon. If the shadow is the shortest, it is the summer solstice; The longest shadow is the winter solstice. The date in 24 solar terms is basically fixed every year. For example, the vernal equinox is generally from March 2 to 22, and the summer solstice is generally from June 2 1 or 22, which are basically fixed.