34. how long does a complete precession cycle take? a) 60,000 years b) 26,000 years c) 6000 years d) 4 years 35. how many astronomical units are there between the earth and sun? a) one b) ten c) one million d) six trillion 36. what was one of the contributions made by copernicus to astronomy? a) he discovered that the planets move around the sun in elliptical orbits, b) he said that the earth is not the center of the universe. c) he developed a theory of gravity that could explain orbital motion. d) he used a telescope to observe the heavens, thereby reinforcing the notion of heliocentricity e) he made extensive and detailed observations of the positions of the planets. 37. what contribution to astronomy was made by tycho brahe? a) he discovered that the planets move around the sun in elliptical orbits. b) he said that the earth is not at the center of the universe. c) he used a telescope to observe the heavens, thereby reinforcing the notion of heliocentricity. d) he made extensive and detailed observations of the positions of the planets. e) he developed a theory of gravity that could explain orbital motion. 38. what was one of the contributions made to astronomy by joannes kepler? a) he discovered that the planets move around the sun in elliptical orbits. b) he developed a theory of gravity that could explain orbital motion. c) he said that the earth is not at the center of the universe. d) he used a telescope to observe the heavens, thereby reinforcing the notion of heliocentricity. e) he made extensive and detailed observations of the positions of planets. 39. what was one of newton's contributions to astronomy? a) he discovered that the planets move around the sun in elliptical orbits. b) he developed a theory of gravity that could explain orbital motion. c) he said that the earth is not at the center of the universe. d) he used a telescope to observe the heavens, thereby reinforcing the notion of heliocentricity e) he mad extensive and detailed observations of the positions of planets. 40. the force of gravity between two objects: a) increases with the mass of the objects and decreases with the distance between them. b) decreases with the mass of the objects and increases with the distance between them. c) increases with the mass of the objects and the distance between them. d) decreases with the mass of the objects and the distance between them.