Download 1. Evolution of the Solar System— Nebular hypothesis, p 10 a

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Evolution of the Solar System— Nebular hypothesis, p 10
a. Cloud of atoms, mostly hydrogen and helium
b. Gravitational collapse contracted it into rotating disc
c. Heat of conversion of gravitational to thermal energy fired Sun
into star in center of nebular cloud
d. Cooling allowed condensation of rocky particles in inner solar
system, that collided to become planets—accretion
i. Their accretion created gravitational heat of contraction—
warm but fairly small
ii. Unable to attract much lighter elements
e. Outer nebular cloud stayed cool
i. Ices of methane, carbon dioxide, ammonia and water
ii. Cooler at greater distances from Sun,
1. these solid particles collided to become outer planets.
2. Large quantities existing there allowed these planets
to become enormous, and attract and hold lighter
elements
Big Bang happened before all of this—
a. created the universe, the early galaxies, and the first-generation
stars
b. Remember, Sun is a second or third generation star—the nebular
cloud of dust and gases was created by a supernova of a preexisting star
Earth Structure
a. Compositionally: Crust, Mantle, Core
i. Most of Earth is mantle—rocky shell 2900 km thick
ii. Crust has less iron, more silica—thin veneer
iii. Core is mostly metal—iron and nickel, ~3500 km radius
b. Physical properties of these zones change with depth, due to
increase in pressure at greater distances from surface
i. Lithosphere is the crust and uppermost mantle that behaves
in a brittle manner (100-250 km)
ii. Asthenosphere is a soft (but not melted) zone of the upper
mantle that the lithosphere moves around on (to a depth of
about 600 km)
iii. Increased pressure keeps the lower mantle rigid to its
boundary with the core.
iv. Outer core is liquid (molten) metal (~2260 km thick)
v. Inner core is under so much pressure that it is solid (1220
km radius)
History of Astronomy—ch 21
a. Ancient civilization ideas that Earth was at the center
b. Age of Reason beginning to recognize Sun is center
c. Age of Technology exploring wide reaches of the universe
History of Astronomy—Early Years
2006, Sept 28
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5.
Ancient Greeks thought planets rotated around Earth in perfect
circles
a. Anaxagoras, 5th century BC, reasoned that Moon had phases
because it is a sphere, and is lighted by Sun
b. Aristotle, tutor of Alexander BC 382-322,
i. knew Earth was round from shadow of Earth during lunar
eclipse
ii. helped cement the Geocentric view of the solar system
because
1. Earth has no apparent movement
2. Things do not fly off the surface
3. Looks like the stars are moving
4. There is no stellar parallax
5. Earth must be stationary
c. Aristarchus BC 312-230
i. Determined relative sizes of Sun and Moon by shadows
during eclipse events
ii. Greater size of Sun lead him to believe Sun was center—
Heliocentric
iii. Believed Earth’s axis was tilted to orbit around Sun, and this
creates seasons
iv. Hypothesis discounted due to observations of Aristotle, etc.
d. Erastosthenes BC 276-194 Librarian in Alexandria
i. Determined size of Earth
1. Found notes indicating Sun is directly overhead in
Syene on summer solstice
2. Sun was about 7o south of overhead in Alexandria
3. this is about 1/50 of a circle, so Earth’s circumference
must be 50x that distance
ii. 39,400 km ~ 40,075 km—pretty good for 2200 years ago
e. Hipparchus
i. Star catalog: Location, Brightness 1-6
ii. Length of year within minutes of actual
iii. Prediction of lunar eclipse events
f. Cladius Ptolemy 85-100 to 165-180 AD
i. Mathematician, geographer, astronomer
ii. His “Great Work” (Syntaxis, Amalgest) preserved by Persian
scholars through middle ages
iii. Geographer
1. Maps were very accurate
2. first known attempt to project sphere onto a plane
3. inspired Columbus
iv. Mathematician—work with circles and chord theorems
v. Codified Geocentric View—model that planets orbit around
Earth
History of Astronomy—Early Years
2006, Sept 28
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1. Perfect circle orbits discounted because of ‘retrograde’
motion with respect to Earth
a. Looks like planet going backward in orbit
b. Actually different speeds of planets orbiting Sun
2. devised idea of ‘epicycles’ to explain this
a. small loops in orbits could explain backward
motion
b. best predictor of location of planets until Kepler
(1609)
c. accepted by Roman Catholic Church, and Church
punished those who reasoned against it
History of Astronomy—Early Years
2006, Sept 28
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6.
Age of Reason
a. Nicolaus Copernicus 1473-1543
i. Commenteriolus manuscript circulated from 1512
1. unpublished
2. Heliocentric hypothesis
ii. ‘On the Revolutions of the Planets’ published year of his
death
1. incorporated some epicycles to account for lack of
perfect agreement with perfectly circular orbits around
Sun (did not consider ellipse shape of orbits)
2. publisher’s preface declared it ‘hypothesis’ to predict
location of planets
3. not much notice taken by Church at that time
4. Galileo began “Copernican Crusade” in early 1600’s
that lead to it being banned from 1632-1835 by
Catholic Church
b. Tycho Brahe 1546-1601 Danish astronomer
i. Observations very exact thorough
1. 1572 Supernova in Cassiopeia
2. Comet in 1577 convinced him Aristotle’s hypothesis
was wrong—celestial sphere not solid and unchanging
ii. “great quadrant” and corrections for refraction of
atmosphere allowed him to plot very accurately
1. calculated Earth’s axial tilt to 1/100 of degree
2. tropical year length to one second accuracy
iii. rejected Ptolemaic system, and Copernican system
1. Tychonian model
a. Sun orbits Earth
b. All other planets orbit Sun
c. Earth is fixed—there is no stellar parallax
iv. Took on assistant Johannes Kepler in 1600
c. Johannes Kepler 1571-1630
i. Used Tycho’s observations to formulate laws of planetary
motion
1. Planets move in elliptical orbits around Sun
2. Planets sweep equal area in equal time period
3. distances of planets to Sun are proportional to period
of orbit around Sun (p2=d3)
ii. fanatic about finding ‘causes’ for natural observations—
hindered him at times
iii. Vigorous supporter of Galileo’s observations of the moons of
Jupiter
History of Astronomy—Early Years
2006, Sept 28
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d. Galileo Galilei 1564-1642
i. Heard about lenses being used to magnify objects
1. created his own telescopes to 30 power—not the
inventor!
2. looked at planets and Sun
ii. Planetary observations
1. discovered planets are discs, not points
2. found Jupiter has moons
a. implication that Earth not the only center of
orbit
b. disputes the argument that if Earth orbits Sun,
then Moon would be left behind
3. Venus has phases, and this supports heliocentric
hypothesis also. He noticed that when Venus is full, it
appears smallest, because it is farther away than
when it is crescent
4. Moon surface is cratered and mountainous
5. Sun has sunspots, that move around on Sun’s surface
iii. Dialogue of the Great World Systems published in 1630,
banned by Church, he was house-arrested for the rest of his
life—exonerated in 1992
e. Isaac Newton 1642-1727
i. Formulated and tested the Law of Universal Gravitation—
every body in the universe attracts every other body with a
force proportional to their masses, and inversely
proportional to the distance between them
ii. Accounted for why Kepler’s laws worked
iii. Also explains perturbations of orbits due to other bodies
f. Foucault’s pendulum proved that Earth rotates on axis
i. Pendulum continues to swing in same plane unless acted
upon by outside influence
ii. Pendulum set into motion changes apparent position over
full day period
iii. It doesn’t really swing in a changing plane, Earth is rotating
under it.
History of Astronomy—Early Years
2006, Sept 28
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