星空有约丨立春日期为啥“变来变去”？

Group 1 - The core point of the article discusses the timing of the solar term "Lichun" (Beginning of Spring), which will occur on February 4, 2025, and its astronomical basis [1][3][4] - The astronomical definition of solar terms indicates that they are specific moments in time, with each term corresponding to the sun's movement along the ecliptic, where every 15 degrees of movement marks a new solar term [3][4] - The concept of different types of years (tropical year, sidereal year, etc.) explains the discrepancies in the calendar dates of solar terms, with a tropical year averaging about 365 days, 5 hours, and 49 minutes, leading to shifts in the dates of solar terms over the years [5][6] Group 2 - The article highlights that the Gregorian calendar and the 24 solar terms reflect the relative motion of the Earth and the Sun, with solar terms generally falling within a few days of their expected dates in the Gregorian calendar [7] - The complexity of lunar calendar dates is noted, as the first day of the lunar year (Spring Festival) varies between January 21 and February 21, which can lead to "Lichun" not always aligning with the beginning of the lunar year [8][9] - Examples of lunar years are provided, such as the upcoming Year of the Horse, where "Lichun" will occur at the end of the lunar year, and the Year of the Snake, which had two occurrences of "Lichun" [9]