Announcements

1
Announcements

• Solutions to Homework 3 are posted on web site.
• Test next week Tuesday, Wednesday, or Thursday
  (your choice) at testing center one hour time
  limit no calculators covers through todays
  lecture, homework 1-3, chapters 1, 4, most of 5.

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Kepler and Galileo

• 11 September 2003

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Today

• How Johannes Kepler found a much more accurate
  scheme for predicting planetary positions, based
  on new mathematical laws
• How Galileo, using the newly invented telescope,
  discovered startling facts about the sun, moon,
  stars, and planets

4
Tycho BraheDanish astronomer, 1546 - 1601
Tycho made highly accurate (within 1/60 degree)
naked-eye observations of the positions of stars
and planets over many years. He proposed a
compromise model in which all the other planets
orbit the sun, but the sun orbits the earth.
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Johannes KeplerGerman astronomer, 1571 - 1630
Kepler worked under Tycho during 1600 - 1601,
then inherited the records of Tychos detailed
observations. He accepted the Copernican
hypothesis, but abandoned the assumption that all
motions are circular.
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The Orbit of Marsbased on Tychos observations
Toward Mars
Earth
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The Orbit of Mars
Earth 1.9 years later
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The Orbit of Mars
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The Orbit is an Ellipse!
Focus
Focus
The sun is at one focus theres nothing at the
other.
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Planets go faster when theyre close to the sun
A line drawn from the sun to the planet sweeps
out equal areas in equal times.
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Outer planets move slower than inner planets.
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Outer planets move slower than inner planets.
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Outer planets move slower than inner planets.
(Time in years)2 (Radius in AU)3
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Keplers Laws

• Orbits are ellipses, with sun at one focus.
• Equal areas in equal times (faster when close to
  sun)
• (Time in years)2 (Radius in AU)3

Bottom line The universe speaks math!
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Galileo GalileiItalian scientist, 1564 - 1642
Made one of the first telescopes, and pointed it
at the heavens . . .
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Siderius Nuncius (The Starry Messenger)Venice,
1610
(Written in Italian, not Latin!)
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Lunar topography . . . Sunspots . . .
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Many new stars . . .
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New planets orbiting Jupiter . . .
At least some planets dont orbit the earth and
earth isnt the only planet with a moon!
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Phases of Venus . . .
Venus, at least, must orbit the sun, not the
earth.
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What happened to Galileo?

• He became famous (not just among astronomers)
• He started advocating Copernicanism (and
  ridiculing those who disagreed)
• Condemned by the Church, placed under house arrest

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A final thought . . .
Copernicus was Polish, Tycho Danish, Kepler
German, Galileo Italian, Newton English. So what?
Science belongs to everyone.