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A Brief History of Planetary Science
Astronomy 311Professor Lee
CarknerLecture 2
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Ancient Astronomy
They noticed that some things moved with respect to the stars: Five “wandering stars” (planets)
Also transient things like comets and meteors
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Caracol
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Ancient Observing
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 Earth’s diameter
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Finding the Size of the Earth
Sunlight
To ZenithTo Zenith
SyeneAlexandria
To Sun7
7
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Eratosthenes’s Experiment• Measure length of shadow,
find angle between Sun and zenith:
• • Subtract angles measured
at both cities: • If D is distance between
the two cities (756km), the circumference of the Earth is:
•
zenith
L=length of shadow
Sun
H =heightof stick
Angle =
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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 Tycho’s data to determine three laws of planetary motion (early 1600’s)
You can predict how they will move
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Galileo’s Observations
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Galileo and the Telescope Made many important observations starting in
1610, including: Mountains on the Moon Phases of Venus
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 Kepler’s Laws
to discover gravity (~1700):
The universe is governed by universal rules
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Discovering the Other Planets
Uranus (William Herschel, 1781) Pluto (Clyde Tombaugh, 1930)
In the the 1990’s large infrared
telescopes confirm a large, well populated, zone of small icy bodies beyond Neptune Called the Kuiper Belt
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Space Missions
A series of space missions since the early 1960’s have allowed close up views of the planets
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
In the 1990’s first detection of planets outside of the solar system
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
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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