Core Points - The winter solstice, occurring on December 21, marks the shortest day and longest night in the Northern Hemisphere, with varying night lengths across different regions in China [1][2] - The length of the night increases from south to north in China, with cities like Harbin experiencing approximately 15 hours and 20 minutes of night, while Haikou has about 13 hours and 5 minutes [1] - Contrary to common belief, the winter solstice is not the day with the latest sunrise or earliest sunset due to the tilt of the Earth's axis and its elliptical orbit around the sun, leading to a phenomenon known as the equation of time [2] Summary by Sections Night Length Variation - Night length increases from southern to northern regions in China, with a maximum difference of over 2 hours between major cities [1] - Specific night lengths for various cities on the winter solstice include Harbin (15 hours 20 minutes), Beijing (14 hours 40 minutes), Nanjing (13 hours 57 minutes), and Haikou (13 hours 5 minutes) [1] Sunrise and Sunset Timing - The earliest sunset occurs in late November to early December, while the latest sunrise will not happen until early January 2026 [2] - The variation in sunrise and sunset times is influenced by geographical location and year, making it non-fixed [2] Cultural Significance - The winter solstice is viewed as the starting point for the return of longer days, symbolizing the rebirth of the sun [2] - It is suggested that photography enthusiasts can capture the sun's position over the seasons starting from the winter solstice to create a visually appealing "figure-eight" pattern [2]

Group 1 - The summer solstice occurs on June 21, marking the longest day of the year in the Northern Hemisphere, with daylight duration increasing as one moves north [1][4] - The term "summer solstice" refers to the moment when the sun reaches its northernmost point in the sky, directly overhead at the Tropic of Cancer, resulting in the shortest shadows at noon [4][10] - Despite the longest daylight duration, the latest sunset does not typically occur on the summer solstice due to the difference between true solar time and mean solar time, with the latest sunset usually happening in late June [7][10] Group 2 - The difference between true solar time and mean solar time is known as the equation of time, which varies throughout the year, ranging from -14 minutes to +16 minutes [7] - After the summer solstice, the ground continues to absorb more heat than it releases, leading to rising temperatures until the end of summer [10] - Ancient Chinese observed shadow lengths to determine seasonal changes, with the phenomenon of "no shadow" occurring at noon on the summer solstice for regions near the Tropic of Cancer [10]