kepler's laws

Johannes Kepler

German astronomer who first stated laws of planetary motion (1571-1630)

eccentricity

The degree of elongation of an elliptical orbit, the shape of Earth's orbit

ellipse

elongated, closed curve that describes Earth's yearlong orbit around the Sun

Kepler's Second Law of Planetary Motion

states that an imaginary line drawn from the sun to any planet sweeps out equal areas in equal time intervals (planets travel faster when they are closer to the sun)

Kepler's First Law of Planetary Motion

states that each planet travels in an elliptical orbit around the sun, and the sun is at one of the focal points

retrograde motion

Apparent backwards motion of the planets in Earth's sky

Tycho Brahe

Danish Astronamer who produced large amounts of astromatical data but believed that other planets rotated around the sun while the sun and moon rotated around the earth

Kepler's Third Law of Planetary Motion

More distant planets orbit the Sun at slower average speeds, obeying the precise mathematical relationship p(squared) = a(cubed)

Galileo Galilei

Scientist who built the first telescope and proved that planets and moons move. Persecuted for supporting Copernicus' ideas

Nicholas Copernicus

He thought that the sun was the center & the plants went around the sun in circles, He believed in a heliocentric, or sun-centered, conception of the universe. He argued that the Sun was at the center of the universe. The planets revolved around the sun.

epicycle

In the Ptolemaic theory, a small circle, riding on a larger circle called the deferent, on which a planet moves. The epicycle is used to account for retrograde motion.