How many days does it take the Earth to revolve around the Sun? The answer to this question and more are answered when using this gear-driven model representing the Sun, Moon, and Earth and their relationships. Daylight, night, seasons, and phases of the Moon are all effectively demonstrated. The arm is 15″ long; Sun is 6″ in diameter; Earth is 4″ in diameter; the moon is 1″ in diameter. Includes Study Guide. Grades 3+, Ages 8+.