The way to Calculate Summer Solstice
Formula: [Y*D+C]-L Note: Y refers to the last two numbers of a year, such as 10 in 2010, 08 in 2008 D=0.2422 L=the number of leap years 21st century C=21.37 20th century C=22.20 Example: The date of Grain Buds in 2088=[88×.0.2422+21.37]-[88/4]=42-22=20, Summer Solstice falls on June 20th. Exceptions: 1928, add one to the calculated result
In the Han Dynasty (260BC-220), when the Mid-autumn Festival and the Double Ninth Festival were not as important as they are today, the Summer Solstice was already celebrated by people. Due to busy farm work, celebrations in that period were simple. Later, the Summer Solstice was turned into a solar term, but is still given close attention.
The Summer Solstice occurs exactly when the Earth's axial tilt is closest to the sun, at its maximum of 23° 26'. Though the Summer Solstice is an instant in time, the term is also colloquially used to refer to the day on which it occurs. Except for the polar regions, where daylight is continuous for half of the year, the day on which the Summer Solstice occurs is the day of the year when an entire hemisphere experiences its longest period of daylight. Thus the seasonal significance of the Summer Solstice lies in the reversal of the gradual shortening of nights and lengthening of days. The summer solstice occurs in June in the Northern Hemisphere, and in December in the Southern Hemisphere.
At the Tropic of Cancer (23°26'N) and all points to the north, and at the Tropic of Capricorn (23°26'S) and all points to the south, the sun reaches its highest position in the sky on the day of the Summer Solstice. However, between the Tropic of Cancer and the Tropic of Capricorn, the highest position of the sun does not occur at the Summer Solstice, since the sun reaches the zenith here and it does so at different times of the year, depending on the latitude of the observer.
Depending on the shift of the calendar, the Summer Solstice occurs some time between December 21 and December 22 each year in the Southern Hemisphere, and between June 20 and June 21 in the Northern Hemisphere. Diagram of the Earth's seasons as seen from the north. Far right: December solstice. Throughout the world, interpretations of the event vary from culture to culture, but most cultures recognize it as a sign of fertility, involving holidays, festivals, gatherings, rituals and other celebrations around that time.