A Brief History of Planetary Science

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A Brief History of Planetary Science

• Astronomy 311
• Professor Lee Carkner
• Lecture 2

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Ancient Astronomy

• They noticed that some things moved with respect
  to the stars
• The Moon
• Also transient things like comets and meteors

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Caracol
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Ancient Observing

• People all over the world built devices to help
  observe the sky
• Two basic purposes
• When does planting season begin?
• Our place in the universe has deep spiritual
  significance

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Ancient Greek Astronomy

• Greeks used reason and mathematics to study the
  sky
• Greek discoveries
• Relative distance to Sun and Moon
• Earths diameter

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Finding the Size of the Earth
Sunlight
To Zenith
7?
To Zenith
To Sun
Syene
Alexandria
7?
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Eratostheness Experiment

• arctan (L/H) q1
• Subtract angles measured at both cities
• Dqq1-q2
• C(360/Dq) X D

Sun
zenith
Angle q
H height of stick
Llength of shadow
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Geocentric Solar System

• Most obvious explanation of fact that everything
  seems to go around the Earth
• Developed between 200BC (Hipparchus) and 200AD
  (Ptolemy)

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Retrograde Motion and Epicycles
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Heliocentric Solar System

• First proposed by Aristarchus (300BC)
• More comprehensive model developed by Copernicus
  (1500 AD)
• Better explains retrograde motion, relative
  brightness and positions of planets

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Uraniborg on the Island of Ven
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Tycho, Kepler and the Motions of the Planets

• His successor Johannes Kepler used Tychos data
  to determine three laws of planetary motion
  (early 1600s)
• You can predict how they will move

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Galileos Observations
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Galileo and the Telescope

• Made many important observations starting in
  1610, including
• Mountains on the Moon
• Galileos writings were condemned by the church,
  but presented hard evidence
• Careful observation and theorizing by Copernicus,
  Brahe, Kepler and Galileo disproved the seeming
  obvious and incontrovertible geocentric model.

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Newton and Gravity

• Isaac Newton used Keplers Laws to discover
  gravity (1700)
• The universe is governed by universal rules

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Discovering the Other Planets

• Careful observation led to the discovery of
• Neptune (Adams and Le Verrier, 1846)
• No other large planets
• In the the 1990s large infrared telescopes
  confirm a large, well populated, zone of small
  icy bodies beyond Neptune

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Space Missions

• We now know compositions, atmospheric properties,
  temperatures, and morphologies for nearly every
  planet
• This data has provided enormous insight into the
  history and nature of the solar system

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Exoplanets
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Extrasolar Planets

• A planets gravity produces a slight periodic
  motion of the central star
• Our solar system is not unique, billions of
  planets in the galaxy

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Next Time

• Meet in planetarium
• Read Chapter 1.1-1.5
• Do homework
• Observing Tonight 9-10 pm
• If clear (check webpage)
• Bring at least two copies of telescope template

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Summary

• Pre-civilized
• Sun, moon and planets move
• Can be used to determine seasons
• Greek (300BC -300AD)
• It is possible to measure their properties
• Copernican Revolution (1500-1700AD)
• Copernicus -- Planets (including the Earth) orbit
  the Sun
• Kepler -- Planets have elliptical orbits and
  their motions are governed by laws
• Galileo -- planets have features like the Earth
  (mountains, satellites)

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• Newton and Physics (1700 AD)
• Planets follow laws of physics
• Gravity accounts for orbital motion
• Modern (20th Century)
• Solar System consists of 9 (now 8) planets plus
  cometary region
• Space missions have allowed the detailed study of
  each planet
• Planets exist around other stars