1. THE EARTH, THE MOON & THE SUN

2. Rotation: Spinning on an axis (Sun, Earth, Moon).
Revolution: A complete trip around an object (Earth, Moon).

3. Orbits Aphelion: Earth is farthest from the sun.
Perihelion: Earth is closest to the sun.
Perigee: Moon is closest to Earth.
Apogee: Moon is farthest from Earth.

5. Kepler’s Laws of Planetary Motion
1st Law: The orbit of a planet is an ellipse with the Sun at one of the two foci. A planets orbit is an ellipse, not a circle.
2nd Law: A line segment joining a planet and the sun sweeps out equal areas during equal intervals of time. The Sun is not at the center but at a focal point of the elliptical orbit.
3rd Law: The square of the orbital period of a planet is proportional to the cube of the semi-major axis of its orbit. Linear and angular speed of a planet is not constant, but the area speed is constant.

6. 1st Law: A planets orbit is more of an oval than circle.
2nd Law: The Sun is off to the side inside the oval.
3rd Law: Planets move in the oval faster if closer to the sun.