An Astronomical Unit (AU) is the average distance
between Earth and the Sun.
Used when measuring distances to other solar system
A Light year is the distance it takes light to travel in
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
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.
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