Why is the Winter Solstice on the Gregorian calendar? Why is the winter solstice on December 21 or 22?

Why is the Winter Solstice on the Gregorian calendar? Why is the winter solstice on December 21 or 22?
In our country, some festivals are celebrated on the Gregorian calendar, while others are celebrated on the lunar calendar. So, let’s take a look at why the Winter Solstice is celebrated on the Gregorian calendar? Why is the winter solstice on December 21 or 22? The eleventh month of the lunar calendar is the winter month, also known as Gu month and Chang month. The representation in the Heavenly Stems and Earthly Branches is also called "Zi Yue" and "Jian Zi". If you want to know about your fortune this month, please visit Mr. Shuimo’s website!

Why is the Winter Solstice on the Gregorian calendar?

The Winter Solstice is one of the 24 solar terms (introduction to the 24 solar terms: Beginning of Spring, Rain Water, Waking of Insects, Vernal Equinox, Pure Brightness, Grain Rain, Beginning of Summer, Grain Full, Grain in Ear, Summer Solstice, Lesser Heat, Greater Heat, Beginning of Autumn, End of Heat, White Dew, Autumnal Equinox, Cold Dew, Frost Descent, Beginning of Winter, Light Snow, Heavy Snow, Winter Solstice, Lesser Cold, Greater Cold), and the 24 solar terms in my country are determined according to the Gregorian calendar, so the time of the Winter Solstice is naturally the Gregorian calendar.
The reasons why the twenty-four solar terms are determined by the Gregorian calendar are:
The 24 solar terms are divided according to the position of the sun on the ecliptic (the orbit of the earth around the sun). Considering the sun starting from the vernal equinox (0 degrees of ecliptic longitude, when the sun shines vertically on the equator), every 15 degrees forward is a solar term; a circle of movement and return to the vernal equinox is a tropical year, which totals 360 degrees, so it is divided into 24 solar terms. The dates of the solar terms are relatively fixed in the Gregorian calendar. For example, the beginning of spring always falls between February 3rd and 5th in the Gregorian calendar. However, in the lunar calendar, the dates of the solar terms are difficult to determine. Taking the Beginning of Spring as an example, it can be as early as December 15th of the previous lunar year and as late as January 15th.

Why is the winter solstice on December 21 or 22?

The winter solstice is the 22nd solar term of the 24 solar terms. The Big Dipper points to Zi, and the sun's ecliptic longitude reaches 270°. It falls on December 21-23 of the Gregorian calendar every year. The winter solstice is the extreme point of the sun's direct southward movement. On this day, sunlight directly hits the Tropic of Capricorn. The sunlight is most inclined to the Northern Hemisphere, and the sun's altitude angle is the smallest. It is the day with the shortest daylight and the longest night in all parts of the Northern Hemisphere. The winter solstice is also the turning point for the sun's direct point to return to the north. After this day, it will "go back", and the sun's direct point will begin to move northward from the Tropic of Capricorn (23°26′S), and the daylight in the northern hemisphere (my country is located in the northern hemisphere) will increase day by day.
The time of the winter solstice is also calculated in a way, which is as follows:
The calculation formula for the winter solstice date (Eastern 8th zone): (YD+C)-L
Formula interpretation: Y=last two digits of the year, D=0.2422, L=leap year number, 21st century C=21.94, 20th century=22.60.

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