Aristotles Geocentric Universe 350 BC

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Aristotles Geocentric Universe ( 350 BC)
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Problems with Geocentric Universe

• Motion of planets occasionally reversed
  direction, referred to as retrograde motion.
• Brightness of planets changed throughout the year

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Retrograde Motion of Mars
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Ptolemys Geocentric Solution ( 140 AD)
Epicycles
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Copernican Heliocentric Solar System
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Copernican Retrograde Motion
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Two Different Views of the Universe

• Copernican Sun-Centered
• (Heliocentric)

• Ptolemys Earth-Centered
• (Geocentric)

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Galileos Observations

• Satellites orbiting Jupiter
• Phases of Venus
• Saturns Ring (handles)
• Craters on the Moon
• Sunspots

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Keplers Laws of Planetary Motion

• Orbits are Ellipses not Circles
• Each planet moves in an elliptical orbit with the
  sun at one focus.
• Equal Areas in Equal Time
• Imaginary line joining sun and planet sweeps out
  equal areas of ellipse over equal intervals of
  time.
• Semi-major axis cubed equals period squared for
  all planets orbiting the sun
• a3 P2

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1. Orbits are Ellipses
Each planet moves in an elliptical orbit with the
sun at one focus. Same is true for any object in
orbit about another (comets, asteroids,
extra-solar planets, binary stars, satellites,
Hubble Space Telescope, etc.). Ellipses are
conic sections, as are circles, parabolas, and
hyperbolas.
Sun
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Conic Sections
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2. Equal Areas in Equal Time
An imaginary line joining the sun and a planet
sweeps out equal areas of an ellipse over equal
intervals of time. Means A planet moves faster
when nearer to the sun, slower when farther from
the sun.
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3. Semi-major axis cubed equals period
squared
Major Axis
a3 P2
Semi-Major Axis
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Keplers Third Law
a3 P2
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Newtons Gravity Explains Keplers Laws
G universal gravitational constant
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Newtons Gravity
r 1AU, average Sun-Earth distance If r
2 AU then Fgrav would be 1/4 as strong If r
10 AU then Fgrav would be 1/100 as strong If r
40 AU then Fgrav would be 1/1600 as strong
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Chronology of Mars Exploration

• 1960 - Marsnik 1, 2
• 1962 - Sputnik 22, 24 Mars1
• 1964 - Mariner 3, 4 Zond 2
• 1969 - Mariner 6 ,7, Mars 69A,B
• 1971 - Mariner 8, 9, Cosmos 419, Mars 2, 3
• 1973 - Mars 4, 5, 6, 7
• 1975 - Viking 1, 2
• 1988 - Phobos 1, 2
• 1992 - Mars Observer
• 1996 - Mars 96, Global Surveyor, Pathfinder
• 1998 - Nozomi, Mars Climate Orbiter
• 1999 - Mars Polar Lander with Deep Space 2
• 2001 - Mars Odyssey
• -----------------------------------------------
• 2003 - Mars Express, Exploration Rovers A, B
• -----------------------------------------------
• 2005 - Mars Reconnaisance Orbiter
• 2007 - Phoenix Scout Mission, Netlanders
• 2009 - Mars 2009 (orbiter, lander, rover)

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Sidereal and Synodic Period
Sidereal Period One orbit with respect to
stars Synodic Period One orbit with respect to
Earth
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Superior and Inferior Planets
Superior Planets Mars Jupiter Saturn Uranus N
eptune Inferior Planets Mercury Venus