1. a diagram that shows the sun at the center of the solar system is known as a? a) geocentric model. b) heliocentric model. c) universe model. d) earth moon sun model. 2. why do the planets not travel in a straight path? . a) the forces of inertia and gravity cause them to move in a elliptical orbit around the earth. b) the forces of inertia cause the planets to move in curved paths around the sun. c) the forces of inertia cause the planets to move in curved paths around the sun. d) the forces of gravity and inertia combine to produced elliptical orbits around the sun. e) all of above.