Originally, this clipart illustrates how geocentric and heliocentric models of the Solar System explain the retrograde motion of planets across the night sky (hence, the epicycle in the geocentric model).
地心和日心系統
astronomy、epicycle、geocentric、helicentric、planets、science、solar system、Space Stuff
天文學、本輪、地心、日心說、行星、科學、太陽系、太空東西
資料來源：openclipart ( https://openclipart.org/ )