1. Models of the Solar System
Earth Science
Prairie School

2. Early Models of the Solar System
More than 2,000 years ago, Aristotle suggested an Earth centered (geocentric) model of the solar system, where everything revolved around the Earth.
Claudius Ptolemy suggested that planets move in small circles (epicycles) as they revolve around Earth.
Copernicus proposed a sun-centered (heliocentric) model of the solar system in AD, where planets move at different speeds and at different distances away from the sun.
Galileo discovered four moons traveling around Jupiter, indicating that objects can revolve around objects other than Earth.

3. Models of the Solar System

4. Kepler’s Laws
Law of Ellipses: each planet orbits the sun in a path called an ellipse.
Elliptical orbits can vary in shape, some are elongated and some are very similar to perfect circles.
The shape of the orbit can be described as its eccentricity, which is the degree of elongation of an elliptical orbit.
Found by dividing the distance between the foci by the length of the major axis.
E=0 for a perfect circle and E=1 for an extremely parabolic orbit.

5. Kepler’s Laws
Law of Equal Areas: Describes the speed at which objects travel at different points in their orbits.
Mars moves faster in its elliptical orbit when it is closest to the sun.
Equal areas are covered in equal amounts of time as the object orbits the sun

6. Kepler’s Laws
Law of Periods: The orbital period is the time required for a body to complete a single orbit. The cube of the average distance (a) of a planet from the sun is always proportional to the square of the period (p).
K x a3 = p2
K is a constant
Distance measured in AU and period is in Earth years.
Scientists can use this equation to figure out how far planets are from the sun, by measuring the orbital periods.

7. Newton’s Model of Orbits
Because a planet doesn’t follow a straight line, an outside force must cause the planet to curve.
Newton called this gravity (attractive force between two objects in the universe)
Gravity pulls an object toward the sun but inertia keeps the object moving in a straight line, leading to the ellipse.
The farther away from the sun, what happens to gravitational pull? How would this change the shape of orbits?

8. Model of the Solar System Activity
Complete part 1 today
Part 2 tomorrow…Earth Day!!
Lab questions are due on Thursday
Thursday: Notes over Formation of the Solar System