Which festival is the alternation of solar terms?

Equinox: It is the midpoint of 90 days in spring. One of the 24 solar terms, around March 20 of the Gregorian calendar every year, when the sun is located at 0 (vernal equinox) of the yellow meridian. On the vernal equinox, the sun shines directly at the equator of the earth, and the seasons in the northern and southern hemispheres are opposite. The northern hemisphere is the vernal equinox and the southern hemisphere is the autumnal equinox.

Summer solstice: June 2 1 or 22 of the Gregorian calendar is the summer solstice every year. On the day of summer solstice, the position where the sun shines directly on the ground reaches the northernmost part of the year, almost directly on the tropic of cancer. At this time, the daylight hours in all parts of the northern hemisphere reach the longest in the whole year. The solstice in summer is the turning point of the sun. After this day, I went back. The direct sunlight point moved southward from the Tropic of Cancer, and the daylight in the northern hemisphere became shorter and shorter day by day. After the summer solstice, the height angle of the sun at noon will also decrease day by day in the Tropic of Cancer and its northern area.

Autumnal equinox: The autumnal equinox is usually from September 22nd to 24th every year. On this day, the sun shines directly on the equator of the earth, so in most parts of the earth, a day is divided into 24 hours, each 12 hour. Near the North Pole (90 north latitude) and the South Pole (90 south latitude), the special phenomenon that "the sun circles on the horizon all day" can be observed on this day.

Winter Solstice: A very important solar term and an important traditional festival in the China lunar calendar. Generally speaking, the time is between 0 and 23, 12, 2 12 in the solar calendar every year. On the solstice of winter, "solstice" is the ultimate meaning, and the spirit of winter storage is so extreme. It contains three meanings: the yin is cold to the extreme and the weather is coldest; When the yang starts, it will force the weather to be cold; The sun moves to the southernmost tip, so the days are the shortest and the nights are the longest.