The World's Tenth Tropic of Cancer Marker Site

On June 21, 2004 (the 93rd year of the Republic of China), the summer solstice in the Northern Hemisphere, the six historical Tropic of Cancer markers erected at the intersection of Bo'ai Road and Shixian Road in Chiayi, Taiwan, were officially inaugurated, making it the tenth place in the world to construct a Tropic of Cancer marker. The Tropic of Cancer marker serves as the boundary between the North Temperate Zone and the Tropic Zone. Arctic/Antarctic Circle markers, Tropic markers, and Equator markers are all globally significant landmarks, used to delineate the five climatic zones: North Frigid Zone, North Temperate Zone, Tropical Zone, South Temperate Zone, and South Frigid Zone. The group of Tropic of Cancer markers in Chiayi City is located at a critical transportation hub in the city's southwest, essentially a collection of intersection landmarks, representing four different years. Although they are small and exquisite, they hold significance for transportation and tourism, historical culture, and earth science education. Currently, an 'illustrated monument' stands on the central median to the northwest. Its marble inscription briefly explains the key points of the markers' establishment, and an accompanying diagram helps visitors fully understand that the Tropic of Cancer quietly passed through this intersection in the late 18th century, and is closely related to the naming of Chiayi. The illustrated monument on the southward drift of the Tropic of Cancer explains that 'the Tropic' is a line of latitude determined by the equivalent value of the Earth's axial tilt (obliquity of the ecliptic) in astronomy. There are three factors causing changes in the Earth's axial tilt: precession, nutation, and polar motion. Additionally, plate tectonics can also cause changes in the Tropic line. Consequently, the Tropic of Cancer is moving southward at a speed of over 14 meters per year, and passed near the northern end of the intersection of Bo'ai Road and Shixian Road in this city in 1788. This intersection is a crucial transportation hub in southwestern Chiayi City. In conjunction with the intersection's landscape improvement project, six historical Tropic of Cancer markers were established here, holding profound historical, cultural, and astronomical science education significance.