Why would an observer out in space see the earth orbiting the sun rather than the sun orbiting the earth? A. The same force that pulls an apple to the earth pulls the earth toward the sun. B. The sun has much more mass than the earth. C. The sun's gravity pulls on the earth, rather than the earth's gravity pulling on the sun. D. The force of gravity decreases with distance. What is Kepler's first law of planetary motion? A. The period of a planet's orbit is proportional to its distance from the sun. B. Planets have circular orbits. C. Planets have elliptical orbits. D. The eccentricity of a planet's orbit is proportional to its distance from the sun