Axis

An imaginary line that passes through a planet’s center and its north and south poles, about which the planet rotates.

Rotation

The spinning motion of a planet on its axis.

Revolution

The movement of an object around another object.

Sun

A large, gaseous body at the center of the solar system.

Moon

A natural satellite that orbits a planet.

Orbit

the path of an object as it revolves around another object in space.

Eclipse

The partial or total blocking of one object in space by another.

Penumbra

The part of a shadow surrounding the darkest part.

Umbra

The darkest part of a shadow.

Geocentric

Term describing a model of the universe in which Earth is at the center of the revolving planets and stars.

Heliocentric

Term describing a model of the solar system in which Earth and the other planets revolve around the sun.

Equinox

Either of the two days of the year on which neither hemisphere is tilted toward or away from the sun.

Solstice

Either of the two days of the year on which the sun reaches its greatest distance from the equator.

Tide

The periodic rise and fall of the level of water in the ocean.

Spring Tide

This means that high tides are higher and low tides are lower than average.

Neap Tide

The tide with the least difference between consecutive low and high tides.

Phase

One of the different shapes of the moon as seen from Earth.

Law of Universal gravitation

The scientific law that states that every object in the universe attracts every other object.