kepler law

6. Kepler’s Laws of Planetary Motion

Kepler’s First Law — Law of Orbits

Planets move in elliptical orbits with the Sun at one focus.

Important points:

• Distance between planet and Sun changes

• Closest point → perihelion

• Farthest point → aphelion

For Earth satellites:

• Closest point → perigee

• Farthest point → apogee

Kepler’s Second Law — Law of Areas

A line connecting a planet to the Sun sweeps equal areas in equal time.

Implication:

Planets move faster when closer to the Sun.

Fastest at perihelion
Slowest at aphelion