Plug in this unit and Illuminate the Sun to effectively demonstrate daylight, night, seasons, and phases of the Moon. The Sun, Earth and Moon revolve around one another on this gear-driven model. The earth and moon are shown in true scale. The scale is 1 inch = 2000 miles. If the sun were to be shown at the same scale, it would be approximately 36 feet in diameter. Arm is 15" , Sun is 6" and the Earth is 4" in diameter.