1) Early models proposed Earth as the center of the universe, but problems were found with this view. 2) Copernicus developed a sun-centered model of the solar system which was later supported by Galileo's observations. 3) Kepler's laws of planetary motion established elliptical orbits and variable planetary distances from the sun.

1. Earth Science An overview of the Solar System

10. Gravity The mechanisms of Newton's law of universal gravitation; a point mass m 1 attracts another point mass m 2 by a force F 2 which is proportional to the product of the two masses and inversely proportional to the square of the distance ( r ) between them. Regardless of masses or distance, the magnitudes of | F 1| and | F 2| will always be equal. G is the gravitational constant.

18. Moon

21. Jupiter