지동설, or the heliocentric theory, is the astronomical model that places the 태양 (Sun) at the center of the 태양계 (solar system). This theory suggests that the 지구 (Earth) and other planets orbit around the Sun, rather than the Earth being the center of the universe, as was previously believed in the 지구중심설 (geocentric theory). The heliocentric model was first proposed by 니콜라우스 코페르니쿠스 in the 16th century and later supported by observations from 갈릴레오 갈릴레이. This revolutionary idea changed our understanding of the cosmos and laid the groundwork for modern astronomy, influencing scientists like 요하네스 케플러 and 아이작 뉴턴.