Group 1 - The summer solstice is the tenth solar term and the fourth term of summer, occurring on June 21, 2025, marking the halfway point of summer [2] - The term "solstice" indicates the maximum solar radiation received at the northernmost point of the Earth, particularly affecting areas north of the Tropic of Cancer [2] - The tradition of eating noodles during the summer solstice is linked to the harvest of wheat in northern regions and the belief that hot noodles can expel dampness from the body [2] Group 2 - The "Three伏天" (Three Fu Days) is a traditional Chinese concept indicating the hottest and most humid period of the year, typically occurring from mid-July to late August [2] - The calculation of the Three Fu Days is based on a dual coordinate system involving the "Geng Day" and solar terms, reflecting ancient wisdom in observing nature [3] - The initial Fu period starts on the third "Geng Day" after the summer solstice and lasts for 10 days, while the middle Fu period varies between 10 to 20 days depending on the number of "Geng Days" between the summer solstice and the beginning of autumn [3][4] Group 3 - In 2025, the initial Fu period will last from July 20 to July 29, the middle Fu period from July 30 to August 8, and the final Fu period from August 9 to August 18, totaling 30 days, categorized as a "short Three Fu" [4] - The calculation system for the Three Fu Days showcases the integration of astronomical observations, climate patterns, and practical life applications, which remains relevant in modern agricultural practices and urban emergency planning [4]