Models of the Solar System *Early Models of the Solar System *Kepler’s Laws.
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Transcript of Models of the Solar System *Early Models of the Solar System *Kepler’s Laws.
Models of the Solar System
*Early Models of the Solar System
*Kepler’s Laws
Aristotle
Early Models of the Solar System
• Aristotle-Greek Philosopher– Geocentric Model: Earth-centered
model of the solar system– The sun, the stars, and the planets
revolve around the Earth– Retrograde Motion-Model could not
explain why some planets sometimes appeared to move backward in the sky relative to the stars.
Claudius Ptolemy
Early Models of the Solar System
• Claudius Ptolemy-Greek Astronomer–Thought planets moved in small
circles, called epicycles as they revolved in larger circles around Earth.
–Epicycles seemed to explain why planets sometimes appeared to move backward.
Nicolaus Copernicus
Early Models of the Solar System
– Nicolaus Copernicus-Polish Astronomer• Proposed model that was sun-centered• The planets revolved around the sun• The planets revolved in the same
direction as the sun, but at different speeds and distances from the sun
Copernicus’ Model and Ptolemy’s Model
Galileo Galilei
Early Models of the Universe• Galileo Galilei-Italian
Scientist–Discovered four moons traveling around Jupiter
–Observation showed him that objects can revolve around objects other than Earth.
Tycho Brahe- Danish Astronomer
Tycho Brahe
• Made detailed observations of the solar system
• After his death, his assistant, Johannes Kepler discovers a pattern and develops three laws to explain planetary motion.
Kepler’s Laws
Kepler’s First Law• Law of Ellipses
– Each planet orbits the sun in a path called an ellipse not a circle
– Eccentricity is the degree of elongation of an elliptical orbit
– Formula: divide the distance of the foci of the ellipse by the length of the major axis
– (e=0 for circular orbit, e=1 for an elongated orbit)
Kepler’s Second Law• Law of Equal
Areas• Speed of which
objects travel at different points in their obits. Whether slow or fast, the area covered is the same.
Kepler’s Third Law
• Law of Periods• Relationship
between average distance of a planet from the sun and the orbital period of the planet.
Kepler’s Third Law Cont’d
Mathematical Formula that describes this relationship:See page 693 in your book
Scientists can find out how far away the planets are from the sun using this law. They measure the orbital periods by observing the planets.
Isaac Newton
Newton’s Model of Orbits
• Inertia: Newton hypothesized that a moving body will stay in motion and resist change in speed or direction until an outside force acts upon it.
• Example: a ball rolling on a smooth surface will continue to move unless a force stops it or makes the ball change direction.
Newton• Named the force that causes the
planets orbital path to curve• Named it gravity• Mass and Distance determines
gravity’s force-the farther away an object is, the weaker the pull (gravitational force) by the larger object.