5. copernican revolution
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Copernican RevolutionCopernican RevolutionJ.T.II OlivarJ.T.II Olivar
Faculty of Arts and LettersFaculty of Arts and Letters
University of Santo TomasUniversity of Santo Tomas11stst Semester AY 2011-2012Semester AY 2011-2012
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Outline of the LectureOutline of the Lecture
The Geocentric UniverseThe Geocentric Universe
The Heliocentric Model of the SolarThe Heliocentric Model of the Solar
SystemSystem The Laws of Planetary MotionThe Laws of Planetary Motion
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The Geocentric UniverseThe Geocentric Universe
To the Greeks, the universe was basicallyTo the Greeks, the universe was basically
the solar system.the solar system.
– The Sun, Earth, Moon and the planets knownThe Sun, Earth, Moon and the planets known
at that timeat that time
The Greeks did not consider the Sun, theThe Greeks did not consider the Sun, the
Moon, and the planets to be part of theMoon, and the planets to be part of the
celestial sphere.celestial sphere.
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Planets do not behave in as regular andPlanets do not behave in as regular and
predictable a fashion as the Sun, Moon,predictable a fashion as the Sun, Moon,
and stars.and stars.
Unlike the Sun and the Moon, the planetsUnlike the Sun and the Moon, the planets
seem to wander around the celestialseem to wander around the celestial
sphere.sphere.
– Greek wordGreek word planetes planetes , meaning “wanderer” , meaning “wanderer”
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Planets never stray far from the plane of Planets never stray far from the plane of
the ecliptic and generally traverse thethe ecliptic and generally traverse the
celestial sphere from west to east, as thecelestial sphere from west to east, as the
Sun does.Sun does.
– They seem to speed up and slow down duringThey seem to speed up and slow down during
their journeys, and at times they even appeartheir journeys, and at times they even appear
to loop back and forth relative to the starsto loop back and forth relative to the stars
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Direct or Prograde, andDirect or Prograde, and
RetrogradeRetrograde Motion in the eastward sense is referredMotion in the eastward sense is referred
to as direct, or prograde motion.to as direct, or prograde motion.
The backward (westward) loops areThe backward (westward) loops are
known as retrograde.known as retrograde.
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The earliest model of the solar systemThe earliest model of the solar system
followed the teachings of the Greek followed the teachings of the Greek
philosopher Aristotle (384-322 B.C.)philosopher Aristotle (384-322 B.C.)
– Geocentric in nature, meaning that Earth layGeocentric in nature, meaning that Earth lay
at the center of the universe and that all otherat the center of the universe and that all other
bodies moved around it.bodies moved around it.
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– In this model, each planet was taken to moveIn this model, each planet was taken to move
uniformly around a small circle, called anuniformly around a small circle, called an
epicycleepicycle, whose center moved uniformly, whose center moved uniformly
around the Earth on a second larger circle,around the Earth on a second larger circle,known as theknown as the deferentdeferent..
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Epicycle and DeferentEpicycle and Deferent
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The full Ptolemaic model required a seriesThe full Ptolemaic model required a series
of no fewer than 80 distinct circles.of no fewer than 80 distinct circles.
Syntaxis or Almagest provided theSyntaxis or Almagest provided the
intellectual framework for all discussion of intellectual framework for all discussion of
the universe for well over a thousandthe universe for well over a thousand
years.years.
– The geocentric model went largelyThe geocentric model went largely
unchallenged until the sixteenth century A.D.unchallenged until the sixteenth century A.D.
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The Heliocentric Model of theThe Heliocentric Model of the
Solar SystemSolar System Nicholas Copernicus rediscoveredNicholas Copernicus rediscovered
Aristarchus’s heliocentric (Sun-centered) Aristarchus’s heliocentric (Sun-centered)
model.model.
– Copernicus asserted that Earth spins on itsCopernicus asserted that Earth spins on its
axis and, like other planets, orbits the Sunaxis and, like other planets, orbits the Sun
– Only the Moon orbits EarthOnly the Moon orbits Earth
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Copernican RevolutionCopernican Revolution
The critical realization that Earth is not atThe critical realization that Earth is not at
the center of the universe is now knownthe center of the universe is now known
as the Copernican revolution.as the Copernican revolution.
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The Foundations of theThe Foundations of the
Copernican RevolutionCopernican Revolution The following seven points are essentiallyThe following seven points are essentially
Copernicus’s own words.Copernicus’s own words.
1.1. The celestial spheres do not have just oneThe celestial spheres do not have just one
common center.common center.
2.2. The center of Earth is not the center of theThe center of Earth is not the center of the
universe but is instead only the center of universe but is instead only the center of
gravity and of the lunar orbit.gravity and of the lunar orbit.3.3. All the spheres revolve around the Sun. All the spheres revolve around the Sun.
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4.4. The ratio of Earth’s distance from the Sun toThe ratio of Earth’s distance from the Sun to
the height of the firmament is so muchthe height of the firmament is so much
smaller than the ratio of Earth’s radius to thesmaller than the ratio of Earth’s radius to the
distance to the Sun that the distance to thedistance to the Sun that the distance to theSun is imperceptible when compared withSun is imperceptible when compared with
the height of the firmament.the height of the firmament.
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5.5. The motions appearing in the firmament areThe motions appearing in the firmament are
not its own motions but those of Earth. Earthnot its own motions but those of Earth. Earth
performs a daily rotation around its fixedperforms a daily rotation around its fixed
poles while the firmament remains immobilepoles while the firmament remains immobileas the highest heavens.as the highest heavens.
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6.6. The motions of the Sun are not its motionThe motions of the Sun are not its motion
but the motion of Earth.but the motion of Earth.
7.7. What appears to us as retrograde andWhat appears to us as retrograde and
forward motion of the planets is not theirforward motion of the planets is not theirown but that of Earth.own but that of Earth.
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Copernicus’s writings on the heliocentricCopernicus’s writings on the heliocentric
universe were placed on the Index of universe were placed on the Index of
Prohibited Books in 1616.Prohibited Books in 1616.
– 73 years after they were first published73 years after they were first published
– Remained there until the end of theRemained there until the end of the
eighteenth centuryeighteenth century
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The Laws of Planetary MotionThe Laws of Planetary Motion
Kepler’s simple laws:Kepler’s simple laws:
1.1. The orbital paths of the planets are ellipticalThe orbital paths of the planets are elliptical
(not circular), with the Sun at one focus.(not circular), with the Sun at one focus.
An ellipse is a flattened circle. An ellipse is a flattened circle.
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2.2. An imaginary line connecting the Sun to any An imaginary line connecting the Sun to any
planet sweeps out equal areas of the ellipseplanet sweeps out equal areas of the ellipse
in equal intervals of time.in equal intervals of time.
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3.3. The square of a planet’s orbital period isThe square of a planet’s orbital period is
proportional to the cube of its semi-majorproportional to the cube of its semi-major
axis.axis.
P P 2 2 (in Earth years) =(in Earth years) = a a 3 3 (in astronomical(in astronomical
units)units)
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Newton’s Laws of Motion andNewton’s Laws of Motion and
GravitationGravitation In 1684, Newton had a discussion withIn 1684, Newton had a discussion with
Edmund Halley about the leadingEdmund Halley about the leading
astronomical problem of the day.astronomical problem of the day.
– Why do planets move according to Kepler’sWhy do planets move according to Kepler’s
laws?laws?
Philosophiae Naturalis Principia Philosophiae Naturalis Principia
Mathematica (The Mathematical Principles Mathematica (The Mathematical Principles of Natural Philosophy) of Natural Philosophy)
– Basis for what is known as NewtonianBasis for what is known as Newtonian
mechanicsmechanics
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11stst LawLaw
– Every body continues in a state of rest or in aEvery body continues in a state of rest or in a
state of uniform motion in straight line unlessstate of uniform motion in straight line unless
it is compelled to change that state by a forceit is compelled to change that state by a forceacting on it.acting on it.
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22ndnd LawLaw
– When a forceWhen a force F F acts on abody of massacts on abody of mass m m , it, it
produces in it an accelerationproduces in it an acceleration a a equal to theequal to the
force divided by the mass.force divided by the mass. – Thus,Thus, a=F/m a=F/m , or, or F=ma F=ma ..
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33rdrd LawLaw
– To every action there is an equal and oppositeTo every action there is an equal and opposite
reactionreaction