#### Transcript of Motion of Celestial Bodies Project

**Motion of Celestial Bodies Project **

**Retrograde Motion**

motion in the direction opposite to the movement of something else

Epicycles

A small circle whose center moves around the circumference of a larger one.

Ellipse

A regular oval shape, traced by a point moving in a plane so that the sum of its distance from two other points (the foci) is constant or resulting when a cone is cut by an oblique plane tht does not intersect the base

Focus

A center of interest or activity

Astronomical Unit

A unit of measurment equal to 149.6 million kilometers the mean distance from the center of the earth to the center of the sun

Orbit Period

The time it takes to complete one full orbit around a celestial body.

Revolution

A single complete cycle of such orbital or axial motion

Rotation

The action of rotating around an axis or center

Inertia

A tendency to do nothing or to remain unchanged

Gravity

The force that attracts a body toward the center of the earth, or toward any other physical body having mass

Kepler's 3 Laws

The path of the planets about the sun is elliptical in shape, with the center of the sun being located at one focus.

An imaginary line drawn from the center of the sun to the center of the planet will sweep out equal areas in equal intervals of time.

The ratio of the squares of the periods of any two planets is equal to the ratio of the cubes of their average distances from the sun.

Retrograde Motion

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