Kepler’s Three Laws of Planetary Motion

2. Law of Areas: The line between the Sun and a planet sweeps out equal areas in equal time intervals

Image from Zeilik & Gaustad (1990)

1. Segments AB and CD are approximately equal to the base of a triangle…...
2. The distance from each of those segments to the Sun can be considered to be the height of each triangle…..
3. Recall that the area, for a triangle, is 1/2(base)(height)
4. It is not too hard, therefore, to believe that the areas of triangles A-Sun-B and C-Sun-D are equal