Earth Systems Science - Solar System

Parallax

An apparent shift in the position of an object when viewed from different locations

Retrograde Motion

The apparent motion of planets when they appear to move backwards (west).

Epicylces

small circular orbits that follow around much larger orbits around the Earth

Claudius Ptolemy

He believed that the Earth was at the center of the Universe, and that the sun and other planets revolved around the Earth.

Nicolaus Copernicus

Polish astronomer who proposed a heliocentric model of the universe

Johannes Kepler

German astronomer who first stated laws of planetary motion and believed in a heliocentric universe.

Terrestrial planets

Mercury, Venus, Earth, and Mars: are solid and rocky

Jovian Planets

Jupiter, Saturn, Uranus, Neptune (gaseous)

Ellipse

A elongated circle, or oval shape, the shape of the planets orbit.

Semi-major axis

half of the longest diameter of an ellipse

Aphelion

point in a planet's orbit that is farthest from the sun

Perihelion

orbital point nearest the sun

Eccentricity

How "squished" an orbit is

Focal points (Foci)

the two points at the center of an ellipse