 # According to Keplers laws the square of the orbital period of a satellite is directly proportional to the cube of the semi-major axis of its orbit. WHY orbital period IS LESS NEAR SUN

10 years ago

Keplers laws refine the model of Copernicus. If the eccentricity of a planetary orbit is zero, then Keplers laws state:

1. The planetary orbit is a circle
2. The Sun is in the center
3. The speed of the planet in the orbit is constant
4. The square of the sidereal period is proportionate to the cube of the distance from the Sun.

Actually the eccentricities of the orbits of the six planets known to Copernicus and Kepler are quite small, so this gives excellent approximations to the planetary motions, but Keplers laws give even better fit to the observations.

Keplers corrections to the Copernican model are not at all obvious:

1. The planetary orbit is not a circle, but an ellipse
2. The Sun is not at the center but at a focal point
3. Neither the linear speed nor the angular speed of the planet in the orbit is constant, but the area speed is constant.
4. The square of the sidereal period is proportionate to the cube of the mean between the maximum and minimum distances from the Sun.