Key Words

• acceleration

• aphelion

• conic section

• conjunction

• deferent

• direct motion

• eccentricity

• ellipse

• elongation

• epicycle

• focus

• force

• geocentric model

• gravitational force

• gravity

• greatest eastern and western elongation

• heliocentric model

• hyperbola

• inferior conjunction

• inferior planet

• Kepler’s laws

• law of equal areas

• law of inertia

• law of universal gravitation