Transcript Slide 1

Kepler’s Three Laws of Planetary Motion
The Law of Orbits – All planets move in elliptical orbits with the sun at one focus.
a
Perihelion
Aphelion
ea
e  0.648
eEarth  0.0167
a = semimajor axis
e = eccentricity of an ellipse – the ratio of the distance from
the center to either focus
and the semimajor axis.
Kepler’s Laws
Simulation
Kepler’s Three Laws of Planetary Motion
The Law of Equal Areas – A line connecting the planet to the sun sweeps out
equal areas in equal times.
Therefore the planet moves faster the closer it is to the sun.
Kepler’s Laws
Simulation
Kepler’s Three Laws of Planetary Motion
The Law of Harmony – The square of the period of any planet is proportional to the
cube of the semimajor axis of its orbit.
T a
2
3
Period vs.
Semimajor Axis
To compare two objects orbiting the same mass
T12 T22
 3
3
a1 a2