1. Concept Question 1
Eudoxus required 27 spheres spinning around the Earth to describe the motion of the Sun, Moon, planets and stars.
Aristotle required 56 spheres to account for this motion.
Why is Aristotle’s scheme recalled as a theory, and Eudoxus’s not?

2. Concept Question 2
Aristotle’s theory had difficulties, as he himself admitted, including apparent variation of the size of the Moon and planets.
Aristarchus, a contemporary of Aristotle’s, proposed a heliocentric theory for the universe.
Why was Aristarchus’s theory found unacceptable?

3. Concept Question 3
It was not until 1837 that Bessel and Struve experimentally demonstrated the existence of stellar parallax.
Why was the heliocentric theory accepted in the 17th century despite the continued absence of observational proof of stellar parallax?

4. Concept Question 4
How does this history of science and the acceptance of new theories connect with your classroom dynamics and student learning?