Transcript Kepler`s Three Laws of Planetary Motions

Johannes Kepler’s Three Laws
of Planetary Motion
Aim: What are Johannes Kepler’s Three
Laws of Planetary Motion?
I. Kepler’s Three Laws of Planetary Motion
A. Ist Law of Planetary Motion
1. Planets travel in elliptical orbits with the
sun at one focus.
a. Planet’s distance from the Sun will
change throughout its orbit
b. Aphelion – point in planet’s orbit where it is
furthest from the Sun.
c. Perihelion – point in planet’s orbit where it
is nearest the Sun.
B. 2nd Law of Planetary Motion (Equal Area
Law)
1. States that each planet moves around the
Sun in such a way that an imaginary line
joining the planet to the Sun sweeps over
equal areas of space in equal periods of time.
C. 3rd Law of Planetary Motion (Harmonic
Law)
1. Period – time it takes a planet to travel
one orbit around the Sun.
2. 3rd Law states that the period (P) of a
planet squared is equal to the cube of its
distance (D) from the Sun. P2 = D3
a. Period must be in earth years
b. Distance from the Sun is expressed
in AU (astronomical units)
3. The further a planet is from the Sun, the
longer its period of revolution.
a. Orbit is larger
b. Planets further away move slower.
(ex: Earth moves 30 km/sec,
Mercury moves 49 km/sec, and
Pluto moves 5 km/sec.)