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Beginning of spring: This is the first of the 24 solar terms. It means to begin to enter the spring, "yang and thorns, everything is spring." After beginning of spring, everything is full of vitality, and the four seasons begin now.

Summer solstice: This day is the longest day and the shortest night in the northern hemisphere. From this day on, it entered the hot season, when everything in the world grew most vigorously. In ancient times, the heart also called this day the northern solstice, meaning the northernmost day when the sun was born. After the summer solstice, the sun gradually moves southward, and the days in the northern hemisphere become shorter and the nights become longer.

Autumnal Equinox: From this day on, the direct sunlight position continues to move from the equator to the southern hemisphere, and the northern hemisphere begins to have shorter days and longer nights. According to China's autumnal equinox theory, this day is exactly half of the ninety days in autumn, so it is called autumnal equinox. But in astronomy, it is stipulated that autumn in the northern hemisphere begins with the autumnal equinox.

Winter solstice: Astronomically speaking, this day is the beginning of winter in the northern hemisphere. After the winter solstice, the direct sunlight gradually moved northward, and the days in the northern hemisphere gradually became longer. As the proverb goes, eating noodles on the solstice in winter will make the day longer.