2. How to calculate the solar term time of the winter solstice?
Pointing at the bucket, the sun longitude is 270, which is the winter solstice. The first month is the first month, November is the second month, and the winter solstice is the 22nd of the 24 solar terms. The winter solstice usually falls on1February 2 1 day or1February 22 in the Gregorian calendar.
Note: The average time method (used before 1645) does not consider the uneven motion of the sun on the ecliptic, which is different from the calculation method of the constant air method (used since 1645), and the specific nodal time of each solar term is different.
Astronomically, the "winter solstice" is the turning point of the sun's southward travel. Because the earth is located near the perihelion before and after the winter solstice, its running speed is slightly faster, which causes that the time for the sun to directly hit the southern hemisphere is about 8 days shorter than that for the northern hemisphere in a year, so the winter in the northern hemisphere is slightly shorter than that in summer.