HIPPARCHUS First well-known magazine of stars. Contained positions and an "estimate" of brightness. (Basis of the Magnitude System used today!) Based on a comparison of his star positions and positions recorded 170 years previously, he discovered the PRECESSION of the Earth. This PRECESSION is the sluggish circular activity of the North and South Celestial Poles with a period of 26,000 years! The North Star (Polaris) has NOT always been the Pole Star!
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Fix Figure 3-15Are we in the "Age of Aquarius?PTOLEMY

PTOLEMAIC (Geocentric) MODEL FOR THE SOLAR SYSTEM

Geocentric mechanism is an Earth-centered device. Problem to settle for the Geocentric system:RETROGRADE MOTION OF MARS!When the position of Mars is tracked over a period of severalmonths, Mars sometimes shows up to relocate "backwards" on the sky!!!
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Fix Figure 2-27These "retrograde loops" perform not always look the same!
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Fix Figure 2-28- - - - - - - - - - - - - - -Ptolemy"s Solution: Planets move on EPICYCLES which relocate along DEFERENTS. The movement alengthy the epicycle produces loops which were supplied to describe the retrograde activity.

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Fix Figure 3-17- - - - - - - - - - - - - - -THE PTOLEMAIC SOLAR SYSTEM
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Fix Figure 3-18Ptolemy also had to define why are Mercury and Venus constantly checked out closeto the Sun and also deserve to NEVER be checked out in the middle of the night.RULE: Center of epicycle for Mercury and also Venus remained on the lineconnecting Earth and the Sun."THE ASTRONOMICAL REVOLUTION"
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After about 1000 A.D., clinical inquiry resurconfronted. About 1340 A.D., "Occam"s Razor" was put forth. Ssuggest put, "Simplicity is better". Over the 1200 years from the acceptance of the Ptolemaic Model, the predictions of the planetary positions came to be even more and even more unsuccessful. This forced presenting even more and even more epicycles.COPERNICUS <1473 -- 1543> Publiburned initially "Heliocentric" or Sun-centered design of the Solar System. But, it still had: 1) All movements being circular. 2) Epicycles. This Heliocentric version can conveniently explain: Retrograde Motion of Mars. Earth catches and passes Mars in its orlittle bit.See the Movie!
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Fix Figure 4-04 Why Mercury and Venus are always close to the Sun. A organic consequence if their orbits are inside the Earth"s orbit.
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Fix Figure 4-07TYCHO BRAHE <1547 - 1601> Believed in the geocentric solar device. Kept extremely exact planet positions over more than twenty years, via the goal of disproving the heliocentric design. Tycho"s "compromise" solar device version, which was not ever before really embraced. Sun goes approximately the Planet and other planets go roughly Sun.
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Fix Figure 4-12JOHANNES KEPLER <1571 - 1630>Inherited Tycho"s planetary position information once Tycho passed ameans (BBD). He offered these information to come with:Kepler"s Laws of Planetary Motion- - - - - - - - - - - - - - - Each earth moves in an ELLIPSE via the Sun at one FOCUS.
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Fix Figure 4-13How to attract an Ellipse The line connecting the Sun and the each earth sweeps out EQUAL AREAS in EQUAL TIME INTERVALS. (This indicates that planets move quicker in their orbits the closer they are to the Sun)
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Fix Figure 4-15 The ratio of the PERIOD of radvancement SQUARED and the SEMI-MAJOR AXIS CUBED is a continuous for all planets! (Note: the size of the earth does not matter!)
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Check it out!GALILEO GALILEI <1564 -- 1642>First to use theTELESCOPEfor Astronomy. His Discoveries: Mountains and also valleys on the Moon.Galileo"s Drawings of the Moon Sunspots on the Sun. Implication: Sun and Moon were IMPERFECT spheres! 4 Moons orbiting Jupiter (the Galilean Satellites) Implication: Tright here are some objects NOT orbiting the Earth!Galileo"s Drawings of Jupiter"s Moons The Phases of Venus Geocentric version (left) predicts only "Crescent Venus" Heliocentric design (right) predicts all phases for Venus.
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Fix Figure 4-19 Galileo oboffered all phases of Venus and also listed the "New Venus" was bigger than the "Full Venus". These observations assistance the Heliocentric model.Imperiods of the Phases of Venus When Galileo was elderly, he was brought to trial by the Church.Galileo "recanted" the Copernican model, which conserved him frombeing shed at the stake. Most believe this was done just so thathe might remain alive and also not that he believed the Geocentric model.He had publiburned all his findings, so tbelow was not should die toprove his arguments supporting the Heliocentric (Sun-centered)Solar System.ISAAC NEWTON <1643 -- 1727> Considered to be the GREATEST Scientist to have lived. Made countless contributions in physics and mathematics. We are just interested in Newton"s Laws of Gravity - - - - - - - - - - - - - - -The FORCE (Pull) between 2 objects is: proportional to the Product of the MASSES.

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inversely proportional to the SQUARE of the separation (created as " d " or " R ")
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" G " is the Universal Gravitational Constant,which is a very little number.Using this Law of Gravity, Newton was able to derive Kepler"sThird Law of Planetary Motion! A actual physical understanding ofthe Solar System was accomplished!Week #3 Notes.Week #6 Notes. Back to The Front Page.