Transcript Models of the Solar System

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 suncentered
• 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.