In his *Astronomia Nova 1609*, Kepler pronounced:

**1st Law** - The orbit of a planet is elliptical and the Sun the source of motion is in one of the foci of this ellipse.

**2nd Law** - The apparent diurnal arcs of one eccentric are almost exactly proportional to the square of their distances from the Sun.

**3rd Law** - The periodic times of any two planets are to each other exactly as the cubes of the square roots of their mean distance.

See Also

**Keplers First Law**
**Keplers Second Law**
**Keplers Third Law**
**Laws**
**Principles**