Early Egyptians thought the solar system was a rectangular box. People in early Greece pictured the universe as a set of crystal-like spheres. Later the solar system was viewed as a set of planets orbiting the Sun. Why has the model of the solar system changed over the centuries?

The questions have been asked in several important state and regional science exams in the United States. For example: TAKS-Texas Assessment of Knowledge and Skills, New York State Educational Department Regents exams, California Standards Test, etc.