CHAPTER 27.2 MODELS OF THE SOLAR SYSTEM
Std. IE 1k- Students will recognize the cumulative nature of scientific evidence
Objective 1: Compare models of the solar systems
Objective 2: Summarize Kepler’s three laws of planetary motion
Objective 3: Describe how Newton explained Kepler’s laws of motion
Models of the Solar System
Geocentric – Earth centered model (Aristotle) the sun, stars, and planets revolve around the
EarthDid not explain retrograde motion - the
appearance of some planets moving backward
Epicycles – small circle movements (Ptolemy) Heliocentric model - the sun the center
(Nicolaus Copernicus)
Objective 1: Compare models of the solar systems
What is the geocentric model? Earth centered model
What is the heliocentric model? Sun centered model
What is the movement of planets in small circles? Epicycles
What is the appearance of planets moving backward in the sky? Retrograde motion
Kepler’s Laws
Johannes Kepler discovered patterns which led him to develop 3 laws that explained planetary motion 1) Law of Ellipses 2) Law of Equal Areas 3) Law of Period
1) Law of Ellipses
1st law - States that each planet orbits the sun in a path called an ellipse (not a circle ) Elliptical orbits can vary in shape (elongated or
circles) Eccentricity – the degree of elongation of an
elliptical orbit
2) Law of Equal Areas
2nd law - states that equal areas are covered in equal amounts of time as an object orbits the sun
It describes the speed at which objects travel at different points in their orbits Ex. Mars moves fastest in its elliptical orbit when
it is closest to the sun
3) Law of Periods
3rd law – states the relationship between the average distance of a planet from the sun & the orbital period of the planet
Scientist can find out how far away the planets are from the sun by using this law
Orbital Period - the time required for a body to complete a single orbit
Objective 2: Summarize Kepler’s three laws of planetary motion
Which of Kepler’s laws states that equal areas are covered in equal amounts of time? 2nd law – Law of Equal Area
Which of Kepler’s laws states that each planet orbits the sun in a path called an ellipse? Law of Ellipses
What is the time required for a body to complete a single orbit? Orbital Period
Newton’s Explanation of Kepler’s Law
Newton used inertia to help explain Kepler’s laws. Inertia - a moving body will remain in motion
and resist a change in speed or direction until an outside force acts on it
Newton’s Models of Orbits
Planets do not follow a straight path Gravity = an outside force that cause the orbit to
curve Gravity exists between any two objects in the
universe Formation of curved orbits
1. Gravitational pull sun pulls objects towards it
2. Inertia keeps the object moving in a straight line
Objective 3: Describe how Newton explained Kepler’s laws of motion
What exists between any 2 objects in the universe? Gravity
What is a body remaining in motion unless acted on by an outside force called? Inertia
What is pulling the planets toward the sun? Gravity
What gives planets their curved orbits? Inertia and gravitational pull