NAME:________________________________________ Period:__________
Kepler’s 3 Laws of Planetary Motion
1. Law of Orbits
Kepler's first law states "all planets
move in elliptical orbits with the Sun at
one focus and the other focus empty".
Applied to Earth satellites, the center of the
Earth becomes one focus, with the other
focus empty.
2. Law of Areas
Kepler's 2nd law, the law of areas, states "the line
joining the planet to the Sun sweeps over equal
areas in equal time intervals". When a satellite
orbits, the line joining it to the Earth sweeps over
equal areas in equal periods of time. Segments AB
and CD take equal times to cover. Therefore, the
speed of the satellite changes, depending on its
distance from the center of the Earth. Speed is greatest at the point in the orbit closest to the Earth,
called perigee, and is slowest at the point farthest from the Earth, called apogee. It is important to note
that the orbit followed by a satellite is not dependent on its mass. In simpler terms, as a planet moves
closer to the sun its speed increases. As the planet moves further from the sun, its speed
decreases.
3. Harmonic Law
Kepler's 3rd law, the law of periods, relates time required for a
planet to make 1 complete trip around the Sun to its mean distance
from the Sun. "For any planet, the square of its period of
revolution is directly proportional to the cube of its mean distance
from the Sun." So, the time a planet takes to complete one
revolution around the sun depends on the planet’s distance
from the sun. The further a planet is from the sun, the more
time it takes.