Transcript Kepler`s Laws PowerPoint

What can the Pringles man teach us
about the orbits of planets?
ECCENTRICITY!
Distance between foci
Length of major axis
Planetary Orbits
Mercury
Venus
What do you observe
about the
orbits/motion of our
planets?
Earth
(Distances and times reproduced to scale)
Kepler’s Laws of Planetary Motion
1. All planets travel in elliptical orbits with the Sun at one
focus.
•The Earth's orbit is so close to a perfect circle that it can't be
distinguished with the human eye.
•Eccentricity = a measure of how elliptical (how far from
being a perfect circle) a planet’s orbit is
More ECCENTRIC =
more “squashed”
Less ECCENTRIC =
more circular
2. Each planet travels in such a way that a line joining the
planet and the sun sweeps equal areas in equal times.
• Also called the law of equal areas. Each of the triangles in
the diagram below will have the same area. Also, the time
it takes for the planet to go from one position to the next
will be equal (in this example, a month).
• When the planet is closest to the Sun, it will travel faster
due to gravity.
• Seeing Kepler's Laws at work
3. Harmonic Motion - Relationship between distance
and period of revolution
• P2 = D3
• P is the period (how long it takes to revolve) in Earth
years, and D is the distance in AU’s
• An “AU” is an astronomical unit, which is the average
distance from the Sun to the Earth.
• The period for a planet to orbit the Sun increases
rapidly with the radius of its orbit. Thus, we find that
Mercury, the innermost planet, takes only 88 days to
orbit the Sun but Pluto requires 248 years to do the
same.