Month: July 2025

ASTRONOMICAL UNIT (AU) – The average distance from the Earth to the Sun, about 93 million miles (150 million km).

ORBITAL PERIOD – The time a planet takes to complete one full orbit around the Sun.

PERIHELION – The point in a planet’s orbit closest to the Sun.

APHELION – The point in a planet’s orbit farthest from the Sun.

ECCENTRICITY – A measure of how stretched an ellipse is; 0 represents a perfect circle, and values close to 1 are highly elongated.

SEMI-MAJOR AXIS – Half of the longest diameter of an ellipse, used to describe orbit size.

ELLIPSE – An elongated circle that defines the shape of planetary orbits.

KEPLER’S THIRD LAW (HARMONIC LAW) – The square of a planet’s orbital period is proportional to the cube of its average distance from the Sun.

KEPLER’S SECOND LAW (LAW OF EQUAL AREAS) – A line connecting a planet to the Sun sweeps out equal areas in equal time intervals.

KEPLER’S FIRST LAW (LAW OF ELLIPSES) – Planets orbit the Sun in elliptical paths with the Sun at one focus.