Kepler's laws of planetary motion describe the elliptical orbits of planets with the sun at one focus, the equal area sweep of planetary orbits, and the relationship between a planet's orbital period and the size of its orbit. The first law relates to energy conservation in gravitational fields, the second law is derived from angular momentum conservation, and the third law links gravitational force and centrifugal force. These principles apply to all planets, including Earth, which has an orbital period of approximately 365.242 days.

2. (1) the orbit of each planet is an ellipse with the Sun at
one focus
(2) the orbital radius of a planet sweeps out equal areas
in equal intervals of time
(3) the ratio of the square of a planet’s period (T2) to the
cube of the semi-major axis of its orbit (a3) is a constant for all the
planets, including the Earth
Kepler’s laws of planetary motion

3. • the orbit of each planet is an ellipse with the Sun at one focus.
• the first law consequence of the conservation of energy of a planet orbiting the Sun under
the effect of a central attraction that varies as the inverse square of distance.
Kepler’s 1st laws of planetary motion

4. • the orbital radius of a planet sweeps out equal areas in equal intervals of time;
• The second law describing the rate of motion of the planet around its orbit follows directly
from the conservation of angular momentum of the planet.
Kepler’s 2nd laws of planetary motion

5. • the ratio of the square of a planet’s period (T2) to the cube of the semi-major axis of its orbit
(a3) is a constant for all the planets, including the Earth
• The third law results from the balance between the force of gravitation attracting
the planet towards the Sun and the centrifugal force away from the Sun due
to its orbital speed. The third law is easily proved for circular orbits
Kepler’s 3rd laws of planetary motion
Semi major axisEarth
T=
365.242
days