describe (approximately): the basic features of planetary motion. [P2.8, P3.2]
state: that
1 The orbits of planets in the solar system are ellipses with the Sun at one focus.
2 The radial line from the Sun to a planet sweeps out equal areas in equal intervals of time.
3 The square of the orbital period is proportional to the cube of the semi-major axis of the ellipse. [P2.8, P3.2]
were deduced empirically: by Johannes Kepler (1571-1630). [P3.2]
were later explained: by Isaac Newton (1642-1727), using Newton's laws of motion and Newton's law of gravitation. [P3.2]
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