JOHANNAS KEPLER -
Developed 3 laws that all planets follow while in
orbit!

WARM - UP

Warm-Up Question Answer…

Kepler’s First Law
 The orbit of the planets are ellipses, with the sun at
one focus of the ellipse.
 Draw the sun and Earth and indicate the direction
of orbit on your paper.

Ellipses and Eccentricity
 The amount of flattening of the ellipse is termed the
eccentricity.
 Circle = 0
 Straight Line = 1

Ellipses
 The sun is not at the center of the ellipse.
 There is nothing at the other focus.

Astronomical Distances
 An Astronomical Unit (AU) is the average distance
between Earth and the Sun.
 Used when measuring distances to other solar system
objects.
 A Light year is the distance it takes light to travel in
1 year.
 Used to measure distances to other stars and galaxies.

Kepler’s Second Law
 The line joining the planet to the Sun sweeps out equal
areas in equal times as the planet travels around the
ellipse.
 As the planet approaches the sun…
 Orbital Speed will Increase
 Gravitational force will Increases
 As the planet travels away from the sun…
 Orbital Speed will decrease
 Gravitational force will decrease

Kepler’s Third Law
 The closer the object is to the Sun the faster its
period of revolution.
 Example:
Earth & Mars Orbit

Get your computer – Log on to our website (orbital motion page)
Three links are at the bottom for Kepler’s 1st, 2nd, and 3rd Law