What does Spring and Autumn mean? When are the vernal equinox and autumnal equinox?

Sacrificing ancestors is usually held at the vernal equinox or autumnal equinox of the lunar calendar every year, so it is often called "Spring and Autumn Sacrifice". The Spring Festival is usually in Tomb-Sweeping Day, and the Mid-Autumn Festival is usually in October of the lunar calendar (before the Double Ninth Festival).

The vernal equinox is the midpoint of 90 days in spring and one of the 24 solar terms. Every year around March 20th, the sun is at 0 (vernal equinox) on the yellow meridian.

The autumnal equinox is the sixteenth solar term in the twenty-four solar terms of the lunar calendar, usually on September 22-24 of the Gregorian calendar every year. On this day, the sun reached longitude 180 degrees and directly hit the equator of the earth. Therefore, in most parts of the world, 24 hours are divided equally between day and night, each being 12 hours. After the autumnal equinox, the direct point of the sun began to enter the southern hemisphere from the equator, and the northern hemisphere began to have shorter days and longer nights, and shorter days and shorter nights in a day; Near the North Pole, there are long nights and stars for six months in a year.