The Origin of Modern Astronomy

1
The Origin of Modern Astronomy

• Seeds chapter 4

2
Objective

• Learn how astronomy developed into a method we
  call science

3
Classical Greek astronomy - Aristarchus

• Aristarchus of Samos (ca 310-230 BC)
• Estimated the sizes distances of the Sun Moon
• First known person to hold the heliocentric view

4
Hipparchus

• Hipparchus (ca 190-120 BC) Hipparcos
• Mapped constellations and estimated star
  brightnesses

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Eratosthenes

• Alexandria (Egypt) ca 284-192 BC
• Measured the Earths size using simple
  observation and geometry

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Aristotle

• Greece 384-322 B.C.
• Philosopher
• Described a geocentric view with crystalline
  heavenly spheres
• His incorrect geocentric view took hold

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Parallax

• Most classical scholars held that the Earth is
  fixed because no parallax could be seen for the
  stars and no motion is felt

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Ptolemy

• Alexandria AD 140
• Developed the mathematics for the geocentric
  model of the universe
• Almagest uniform circular motion with epicyle,
  deferent equant

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Geocentric model

• The Sun and planets were supposed to orbit Earth

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Retrograde motion

• The backward looping motion of some planets had
  to be explained

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Geocentric model

• Ptolemys model began a trend of using a
  geocentric description with complex additions of
  circular motions

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Astronomy during the European Dark Age

• During the European middle ages classical
  astronomical knowledge was preserved by Arab
  scholars
• In China, scholars kept observing sky omens eg
  Guest Star SN AD1054
• The Mayans developed an astronomical calendar

Chinese guest star record (1300BC)
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European astronomy advances

• Copernicus 1473-1543 (Poland)
• Heliocentric model with circular orbits
• Opposed the churchs geocentric doctrine
• Not good enough at predicting planetary positions

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Retrograde motion simply explained

• The heliocentric model provided a simpler scheme
  for explaining the motion of Mars and other outer
  planets

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Tycho Brahe

• b.1546 Denmark
• Superb observations of planetary positions
• New Star 1572
• Developed his own geo/heliocentric Tychonic
  model
• Hired Kepler

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Kepler

• b.1571 (sw Germany)
• Mathematician who developed 3 laws of planetary
  motion
• Theory matched observations, putting the
  heliocentric model on a firm basis

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Keplers laws

• Elliptical orbits
• Planet sweeps equal areas in equal time
• Period distance from the Sun are simply
  related P2 a3

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Galileo

• b. Pisa 1564
• Telescopic observations of
• Lunar craters
• Milky Way stars
• Jovian satellites
• Sunspots
• Venusian phases
• Heliocentric defender

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Newton

• b. 1642(3) England
• Three laws of motion
• Law of gravity F G Mm / r2which
  explained Keplers laws etc...

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Newtons laws of motion

• 1. Bodies stay at rest or in uniform motion,
  unless compelled to change by a force.
• 2. Force mass x acceleration
• 3. To every action there is an equal and opposite
  reaction.