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“Motions” in the Heavens
Fixed Stars, Moving Planets
• Stars remain in fixed positions
with each other
– Constellations (groups of stars)
• Planets “wander”
with respect to stars
– Retrograde Motion
Aristotelian Geocentrism
• Earth is center of Universe
– Concentric celestial spheres in which the Sun,
Moon, and stars are imbedded like jewels
– Unblemished, symmetrical Universe
– People don’t fall of
the Earth as it moves…
– Parallax
• Not observed in stars
– Did not explain
retrograde motion
Copernicus, 1530
• Heliocentric – Sun,
center of Solar System
• Explained retrograde
motion
Tycho Brahe, Johannes Kepler
• Brahe: Mapped positions of known bodies
– Could predict where any planet would be seen in
near future
– Drank himself to death
• Kepler: Planets move in elliptical orbits
– Brahe’s student
– Mathematical formulae to describe motion
Galileo vs. Aristotle
• “Law of Inertia” and falling off the Earth
• The Milky Way as a collection of stars (not a
cloud of light)
• Jupiter’s Moons vs. Geocentrism
Ganymede
Io
Galileo vs. Aristotle
• Sunspots and Lunar Maria
– Not “homogenous unblemished bodies”
Isaac Newton
• Popular myth: Isaac Newton invented gravity
• A moving body travels in a straight path unless
acted on by an outside force
– Gravity between Sun and planets makes for
elliptical orbits
The Earth-Moon System
The Lunar Orbit
Phases of the Moon
Eclipses
VS
Red Shift
• Works for sound or light
– If the object is moving
toward you, it will have a
higher frequency (waves/s)
• Louder (sound)
• Bluer (light)
– If moving away (lower
frequency):
• Softer (sound)
• Redder (light)
The Big Bang Theory
• All matter and energy
compressed into single
inconceivably dense point
• Universe expands and thins to
form the galaxies and stars
• 13.7 billion years old
“explosion”
Nebular Hypothesis
• Origin of solar system traced to rotating
clouds of gas + fine dust
– 1755, Immanuel Kant
– Nebulae (“fog” or “cloud”)
– Mostly hydrogen and helium
– These two elements make up all but small
fraction of Sun
Gas and very fine
dust particles
Temperature rises to millions of degrees
Nuclear fusion begins  H atoms combine to form Helium
 sunlight!
Some Rocky Bits Are Left
• Most rocky bits have
been swept away
(accreted onto forming
planets)
• Now, rocky bits that are
left are basically trapped
due to gravity
Asteroid Belt  trapped between
Mars (4) and Jupiter (5)
Asteroid
Belt
The SS at a glance…
• 4.6 billion yrs old
• All planets, at first, were composed of gas
• Protoplanets closest to sun were hot—gasses
moving fast enough to escape gravitational
pull of Pplanet
• Solar wind—a stream of particles originating
from the sun—pushed gasses from inner SS
to outer
• Terrestrial planets vs. Jovian planets
Terrestrial planets
Jovian Planets
Dwarf Planets
The Terrestrial Planets…
Mercury
• Closest planet to the
sun
• Smallest planet
– radius = 2,400 km
• 1 mercury year = 88
earth days
• Spins slowly on its axis
– One day on mercury = 59
earth days
– Insane temp. differences
• Side facing sun = 427°C
• Far side = - 175°C
– Thin He atmosphere
– Magnetic field—possibly
created by liquid core
1. Solid crust (100-300 km thick)
2. Silicate Mantle (600 km thick)
3. Molten Iron Core (1800 km radius)
Mercury Geology
• Mariner 10
• Impact craters
• Caloris baisn-1550 km
wide—impact so powerful,
planetary scale effects—
weird terrane
– Intercrater plains—heavily
cratered plains between
large impact craters
– Smooth plains—similar to
lunar mare—lava filled
depressions
– Compression folds—long,
linear folds caused by
partial cooling of interior
Terrestrial Planets:
Venus
• 108 million km from sun
• Very similar in size to
Earth—radius 6052 km
• Dense atmosphere of
CO2—sulfuric acid clouds
• Atmospheric pressure at
surface = 92 times that of
Earth
• One year on Venus = 224
earth days
• Spins slowly on axis
– One Venusian day = 244
earth days
• Mean surface temp =
460°C
Radar image of Venus
Venus: UV
True color photo of Venus
Studying Venus
• Spacecraft
– Russian Venera project
• V1 and 2—flyby
• V3—crashed into surface
• V4—probe—accurate atm temp, pressure, and comp—ran out of
power
• V5 and V6—crushed by atm pressure
• V7—crashed
• V8—landed and took temp, atm comp and pressure readings for
50 min
• V9 and V10—sent first images of surface—survived only 93
minutes
• V11-12—detected electrical storms
• V13-14—first color pictures
• V15-16--orbiters
Studying Venus Cont…
• Magellan—1989
– Radar mapped 99% of
Venusian surface
• Strange observations
– Only 1000 pristine impact
craters—absence of small
(<2km) craters
– 167 >Mt. Everest sized
shield volcanoes
• Pancake domes—caused by
mantle plumes
– 60% of surface is flat
– No evidence of plate
tectonics—can explain lack
of magnetic field
Why is Venus so hot?
• Venus and earth probably had similar
atmospheres
• Closer proximity to sun = higher mean
temperatures
• Too hot for water to condense
• No oceans = no way to remove CO2 from
atmosphere
• CO2 + water vapor = runaway greenhouse effect
• Water vapor boiled off into space
Terrestrial Planets:
Earth
Everyone should now
know more about Earth
Than any other planet
in the Solar system…
Terrestrial Planets:
Mars
• 150 million km from sun
• About half the size of
earth (3400 km radius)
• Cold
– Average temp = -56°C
– Temps at poles can drop
below -120°C
• Dry
– If you were to condense
all water vapor in
atmosphere—global
layer only 1 mm thick
(Earth 3 km)
• Thin, CO2 atmosphere
• 2 moons
– Phobos and Deimos
Phobos
Deimos
Studying Mars
• Originally, mars was believed
to have oceans
– Poor resolution of early
telescopes
– Human eye predisposed to
discerning lines
• Viking project—mapped
surface
– Viking I and II—landers—
returned first color photos of
surface
• Mars Global Surveyor—very
successful orbiter—
photographed most of the
Martian surface
• Spirit and Opportunity
landers—still operational
Geology of Mars
• Old heavily cratered plains
and young, flat, crater poor
volcanic plains
• Tharsis bulge--four huge
shield volcanoes
– Olympus mons—largest
volcano in SS (25 km tall, 500
km wide)
• Tectonic scheme similar to
Venus—dominated by
volcanism and mantle
plumes
– Valles Marineris—a large
tectonic crack in the martian
crust—caused by cooling of
planet and by uplift in Tharsis
region--
Wind and Water on Mars?
• Liquid water is unstable
on the martian surface
• Ice caps
– Water ice covered by dry
ice (CO2)
• Permafrost from poles to
60°Latitude
• Evidence of large floods
– Eastern portion of Valles
Marineris
• Dust devils
• Dust storms
Martian dust devils