The three sphere instrument consists of a glowing solar sphere, a tilted and rotating Earth model, and a lunar model revolving around the Earth. Driven by a built-in motor, it can automatically, continuously, and accurately demonstrate the relative motion between the Sun, Earth, and Moon and the various astronomical phenomena they generate. It can visually display the changes of day and night and the alternation of seasons. When the three spheres are in the same straight line, the formation process of solar and lunar eclipses can be observed. By using the inclination angle of the Earth's axis, the polar day and night phenomena in polar regions can be explained. It is equipped with season pointers and moon phase disks for real-time reading in the classroom.