History of Astronomy

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History of Astronomy

• Major David Rogers
• USAF (Ret)

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MILITARY MATH

• Multiply the numerical designation of the Osprey
  times the number of major parts to the space
  shuttle.
• Multiply this by the numerical designation of the
  Hercules to this number
• Divide this by the numerical designation of the
  Falcon
• Divide this number by the sum of the numerical
  designation of the Lancer and the AWACS
• Now add 25 of the numerical designation of the
  Lancer

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MILITARY MATH ANSWER

• Multiply the numerical designation of the Osprey
  times the number of major parts to the space
  shuttle. (22 x 4 88)
• Multiply this by the numerical designation of the
  Hercules to this number (88 x 130 11,440)
• Divide this by the numerical designation of the
  Falcon (11,440/16715)
• Divide this number by the sum of the numerical
  designation of the Lancer and the AWACS
  (715/4178.75)
• Now add 25 of the numerical designation of the
  Lancer (178.75.25179)

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New Aircraft

• A-10
• Thunderbolt II
• Warthog
• Mission CAS
• Close Air Support
• Features
• 30 MM Gun
• Maverick Missiles
• Dumb bombs
• Highly maneuverable and heavily armored
• Speed 420 mph

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Todays Lesson

• Renaissance (1400 to 1650) Who were the major
  players in developing todays theory of the solar
  system?
• Copernicus
• Tycho Brahe
• Johannes Kepler and his three laws
• Galileo Galilei

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Modern Astronomys Roots

• Our ancestors looked to the sky to understand
  themselves and their Earth.
• Many people thought the Sun and planets revolved
  around the Earththey were wrong!
• Eventually, they understood the Sun is the center
  of the solar system and that planets orbit the
  Sun.
• But religious teachings at the time promoted an
  Earth-centered view.

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Four People to Know

• During the Renaissance period in astronomy, four
  people established the way we see our solar
  system.
• Nicolaus Copernicuschallenged earlier theories
  of a geocentric (Earth-centered) solar system.
  Even though he was right, the church and many
  scientists didnt accept his ideas.
• Tycho Brahemade amazing observations of space
  from his heavenly castle. After losing his
  nose in a sword fight, wore gold and other
  replacement noses.

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Two More

• Johannes Keplermade sense of Brahes
  observations and created the three basic laws
  that guide our understanding of the solar system
  today!
• Galileo Galileiused a telescope to observe the
  Moon, Sun, Venus, Mars, and Jupiter. Recorded
  details long before others and proposed key ideas
  that supported the Sun-centered view of our solar
  system.

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What did Copernicus believe?

• Nicolaus Copernicus (1473?1543), couldnt make
  sense of centuries of data with Ptolemys
  geocentric (Earth-centered) model.
• Copernicus believed in Aristarchuss heliocentric
  model, with the Sun at the center of the solar
  system.
• His key clue was that the geocentric model didnt
  explain the planets retrograde motion, but the
  Sun-centered model did.

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What is retrograde motion?

• Simply put where celetial objects appear to move
  backward
• Heliocentric models explain retrograde motion as
  a natural result of two planets (one being the
  Earth) passing each other.
• When we first see Mars (point 1middle right)
  from Earth (point 1lower right), Mars appears to
  be at point 1 in the night sky.
• From Earth at point 2, we see Mars point 2middle
  right, and it shows as point 2 in the night sky.
• But because Mars and Earth are orbiting the Sun,
  Mars appears to have changed direction at point 4
  in the sky. This is an example of retrograde
  motion.

QuickTime Movie
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What is the heliocentric model?

• The heliocentric view holds that the Sun is the
  center of the solar system and the planets orbit
  around it.
• Copernicus was able to calculate the distance of
  the planets from the Sun with amazing accuracy by
  using basic geometry.
• Copernicus also had problems
• The church at the time wasnt ready to accept a
  Sun-centered solar system because much of what
  they taught depended on Earth being the center.
• His model couldnt explain the planets locations
  any better than Ptolemys.
• But his theory WAS simpler (remember Occams
  razor?) and he was right!

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What did Tycho Brahe do?

• Tycho Brahe (1546?1601) was a Danish nobleman who
  added a lot to our understanding of planetary
  motion.
• He designed and built instruments far more
  accurate than any other yet made.
• He made observations (supernova and comet) that
  suggested the heavens were more changeable and
  more complex than people had believed. He was
  right!
• He proposed a different geocentric modelearth as
  the center of the universe.

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Who was Johannes Kepler?

• Johannes Kepler (1571?1630) was a young assistant
  to Tycho Brahe.
• After Brahes death, his data passed to Kepler,
  who found he could explain planetary motion based
  on Brahes information!
• Kepler studied it to make three observations
  about planetary motion, which weve come to know
  as Keplers Laws.

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What is Keplers first law?

• Keplers first law says the planets move in
  elliptical orbits with the Sun at one focus of
  the ellipse.
• In the upper shows the motion of the planet.
• In the lower diagram you can see the Sun at one
  focus.

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What is Keplers second law?

• Lets talk first about tetherball. The yellow
  circle in the diagram is the tetherball pole, and
  the black circle is a tetherball on a rope.
• If the rope is long and you hit the tetherball
  hard, the ball is far away from the pole and
  traveling fairly slowly (right side of diagram).
  But as the rope wraps around the pole, the ball
  gets closer to the pole (left side) and goes
  faster!

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What is Keplers second law?

• Keplers second law tells us something similar
  about a planets orbiting speed.
• As planets orbit the Sun, they go slower when
  they are far away from the Sun and faster when
  they are closer to the Sun.

The red circle represents a planet. When its
closer to the Sun, it is going faster and
therefore moves farther during a 6-month period.
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What is Keplers third law?
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• Keplers third law basically says the larger a
  planets orbit, the more time it takes to make
  one complete revolution.
• This is just like driving on a racetrack. As the
  track gets bigger, we take longer to get
  completely around it.
• Kepler was able to predict EXACTLY how much time
  each planets orbit would take (but the math gets
  complicated).

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Keplers Three Laws Again

• The planets dont move in circles they move in
  ellipses around the Sun.
• The closer a planets orbit takes it to the Sun,
  the faster it moves.
• The farther a planet is from the Sun, the longer
  it takes to complete its orbit.

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Galileo GalileiA Radical Thinker

• Galileo Galilei (1564?1642) was active during
  Keplers time. He was the first person to use a
  telescope to study the heavens (including Venus
  and Mars)
• The Moons surface has features similar to
  Earths, so the Moon is a ball of rock.
• The Sun has spots, so the Sun isnt perfect It
  changes its appearance and rotates.
• Jupiter has four objects orbiting it. The
  objects are moons and they arent circling Earth.
• The Milky Way contains an uncountable number of
  stars, so an Earth-centered model is too simple
  to describe our universe.

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Were Galileos ideas accepted?

• No. He was brought before public questioning and
  put under house arrest for the rest of his life.
• Why? Because his views of the solar system
  didnt agree with the widely accepted, but wrong,
  views of the universe held by church and state!

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Lesson review

• Which key people changed the way we understand
  the Earth, Sun, and planets?
• Copernicus, Brahe, Kepler, and Galileo were great
  contributors during the Renaissance.
• What idea did Copernicus develop and promote?
• Copernicus promoted the idea of a Sun-centered
  (heliocentric) solar system instead of the widely
  accepted Earth-centered (geocentric) solar
  system.
• He also used basic geometry to measure very
  accurately the relative distances of the planets
  from the Sun.

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Lesson review (contd)

• What is a heliocentric model?
• A heliocentric model holds that the Sun is the
  center of the solar system and the planets
  revolve around it.
• How did Tycho Brahe contribute to our
  understanding of space?
• Brahe carefully observed and recorded the
  planets locations each night for yearscreating
  a huge set of information on planetary motion.
• He couldnt explain the motion but still
  supported the geocentric theory. He died before
  he could pull everything together.

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Lesson review (contd)

• What are Keplers three laws?
• The planets dont move in circles they move in
  ellipses around the Sun.
• The closer a planets orbit takes it to the Sun,
  the faster it moves.
• The farther a planet is from the Sun, the longer
  it takes to complete its orbit.
• How did Galileo Galilei help us understand the
  solar system?
• He observed the Moon, Sun, Mars, Jupiter, and
  Venus and developed theories that supported the
  Sun-centered or heliocentric view of our solar
  system.

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ActivityQuestions for review

• What is one way Copernicus added to our
  understanding of planetary motion?
• What is one way Brahe added to our understanding
  of planetary motion?
• What is one way Copernicus added to our
  understanding of planetary motion?
• What is one way Galileo added to our
  understanding of planetary motion?
• What is retrograde motion?
• What does it mean to be heliocentric?
  Geocentric?

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ActivityTest yourself

• Write down Keplers three laws in any order.
• Draw a diagram that shows what any one of
  Keplers laws tells us about a planets motion.
• State what main thing kept the heliocentric
  theory from catching on when Copernicus first
  developed it.

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Summary

• What did Copernicus believe?
• What is a heliocentric model?
• How did Tycho Brahe contribute to our
  understanding of space?
• What are Keplers three laws?
• How did Galileo Galilei help us understand the
  solar system?

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Next

• With a general understanding of our solar system
  in mind, you can step outside and enjoy a little
  backyard astronomylearning to find and track
  planets, stars, and constellations.