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GEOCENTRIC
vs.
HELIOCENTRIC
Age of Enlightenment
A cultural movement of
intellectuals in the 17th and
18th centuries, which began
first in Europe and later in the
American colonies. Its purpose
was to reform the way of
thinking using reason, challenge
related to tradition and faith,
and advance knowledge
through the scientific method.
It promoted scientific thoughts,
skepticism and intellectual
interchange and completely
opposed any kind of
superstition, intolerance and
some abuses of power by the
church and the state.
It starts with Scientific Revolution
• The Enlightenment
starts with the
Scientific Revolution
• People started to
question ideas that had
been accepted as facts
for hundreds of years
Back then, all knowledge
came from the Catholic Church
The Catholic
Church and the
Bible were the
source of what
was true and false
in the world
Also…
Ancient Greek
and Roman
Philosophers,
such as Aristotle,
said what was
true about the
natural world
Scientific Revolution
• Was a new way of
looking at the
natural world
• Traditional ideas
were found to be
wrong through
observation,
experimentation,
and theories
GEOCENTRIC
GEO = EARTH CENTRIC = CENTER
They believed the Earth was the center of the universe
HELIOCENTRIC
HELIO = SUN CENTRIC = CENTER
They believed the sun is the center of the universe
Aristotle
The spherical Earth is
at the center of the
universe, and all other
heavenly bodies are
attached to 47–56
transparent concentric
spheres which rotate
around the Earth.
Ptolemy
90-178
Ptolemy argued that
the Earth was in the
center of the universe,
from the simple
observation that half
the stars were above
the horizon and half
were below the
horizon at any time
Nicolaus Copernicus
All the spheres revolve
about the sun as their midpoint, and therefore the sun
is the center of the universe.
What appear to us as
motions of the sun arise not
from its motion but from
the motion of the earth and
our sphere, with which we
revolve about the sun like
any other planet. The earth
has, then, more than one
motion.
1473-1543
Johannes Kepler
Kepler's Three Laws can be used
to describe the motion of the
Planets:
1. The Planets move in orbits
about the Sun that are ellipses
2 . The planets move such that
the line between the Sun and the
Planet sweeps out the same area
in the same area in the same time
no matter where in the orbit.
3. The square of the period of the
orbit of a planet is proportional to
the mean distance from the Sun
cubed.
1571-1630
Tycho Brahe
A Danish astronomer who made measurements of the planet and
stars. His measurements were the most accurate that had yet been
made.
Tycho proposed a system in which all of the planets except for Earth
orbited about the Sun. He claimed that the Sun still orbited about the
Earth, however.
Sir Isaac Newton
Newton derived the law of
gravitation between two
masses. Since the Sun was
the most massive object in
the planetary system, all of
the planets would naturally
be attracted to it and revolve
around it, in the same
manner as the Moon
revolves around the Earth.
1642-1726
Galileo Galilei
Galileo's observations
strengthened his belief in
Copernicus' theory that
Earth and all other planets
revolve around the Sun.
Most people in Galileo's
time believed that the Earth
was the center of the
universe and that the Sun
and planets revolved
around it. 1564-1642
Galileo
Galileo wrote about his
observations and thus
angered the Roman
Catholic Church. The
Church eventually placed
him under house arrest.
The Inquisition was the
tribunal of the Roman
Catholic Church at this
time. The Inquisition
made Galileo kneel
before them and confess
that the heliocentric
theory was false.
Galileo was right all along
In 1992, the Roman
Catholic Church finally
repealed the ruling of
the Inquisition against
Galileo. The Church
gave a pardon to
Galileo and admitted
that the heliocentric
theory was correct. This
pardon came 350 years
after Galileo's death.
Geocentric
• Key Ideas:
– “Geo” = Earth
– “Centric” = Center
• “Earth-centered”
– Earth is the center of the
solar system
– Earth is stationary (not moving)
and everything is moving around us
In your notes, draw a picture of
what the geocentric model looks like…
Geocentric models
• Key Limitations:
– Did not explain the
apparent motions of
some planets (for
example, Mars)
– Did not explain all of
Earth’s motions,
including how a freelyswinging pendulum
moves
Heliocentric
• Key Ideas:
– “Helio” = Sun
– “Centric” = Center
• “Sun-centered”
– The Sun is the center of the
solar system
– Earth rotates on its own axis
AND revolves around the Sun
In your notes, draw a picture of
what the heliocentric model
looks like…
Heliocentric models
Key Limitations:
The early models used circular orbits  did not
explain the apparent motions of planets
(BUT… once elliptical orbits and planets’
orbital speeds were added to the model,
the planets’ apparent motions could be
explained and even predicted!)