An astronomical unit (AU) is the average distance between the Earth and the Sun, approximately 149.6 million kilometers (93 million miles). It is commonly used to describe distances within our solar system.
Kepler's Laws: Three laws describing planetary motion, formulated by Johannes Kepler.
Semi-Major Axis: The longest diameter of an ellipse, half of which defines 1 AU for Earth's orbit.
Eccentricity: A measure of how much an orbit deviates from being circular.