Old Huangli hand-painted Houyi

The vernal equinox is the midpoint of 90 days in spring. One of the twenty-four solar terms, every year on February15th of the lunar calendar (about March 20th -2 1 of the Gregorian calendar), when the sun is located at 0 (vernal equinox) of the yellow longitude. On the vernal equinox, the sun shines directly on the equator of the earth, and the seasons in the northern and southern hemispheres are just the opposite. The northern hemisphere is the vernal equinox and the southern hemisphere is the autumnal equinox.

The summer solstice is one of 24 solar terms, which falls on June 2 1 or 22 of the Gregorian calendar every year. On the day of summer solstice, the sun moves to 90 degrees of the yellow meridian (in Gemini), and the position where the sun directly hits the ground reaches the northernmost point of the year, almost directly on the tropic of cancer. At this time, the sunshine time in the northern hemisphere is the longest.

The autumnal equinox is the sixteenth solar term in the twenty-four solar terms of the lunar calendar, usually on September 22nd or 23rd every year. The climate in the south began to decline from this solar term. First, the sun reaches 180 degrees on this day and points directly at the equator of the earth, so the day is divided into 24 hours, each 12 hour; There is no extreme day and night phenomenon in the world.

Winter solstice is an important solar term in the China lunar calendar, and it is also a traditional festival of the Chinese nation. The winter solstice is usually called "Winter Festival", "Solstice Festival" and "Asian New Year". As early as 2500 years ago in the Spring and Autumn Period, China observed the sun with Tugui, and determined the earliest winter solstice among the 24 solar terms, with the time between 0 and 23 in Gregorian calendar 65438+February 265438.