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34 Cards in this Set

  • Front
  • Back
In science, what two things define beauty?
Symmetry & Simplicity
What were some of the uses of ancient cosmology?
Calendars, navigation, religion, myths, astrology.
What were some of the ancient calendar observatories?
Stonehenge, the Great Pyramid of Giza, Chichen Itza, Bighorn Medicine Wheel
How did the ancient Greeks determine that the moon is a sphere?
Because the terminator (line separating the dark and light side of the moon) is curved
Describe the ancient Greek view of the universe.
It was geocentric - Earth was at the center and stationary.
What reasons caused the Greeks to believe that the Earth was stationary?
-we don't feel the earth move
-no strong winds felt
-what would keep it spinning?
-no parallax observed
-didn't understand inertia and relative motion
-gives central importance to humans
-changing distance of stars not observed
What were some of the incorrect assumptions of Ancient Greeks?
-celestial objects were perfect and made of aether (quintessence)
-only most symmetrical patterns (circles and spheres) apply to shapes & motions of celestial objects
-distance to stars are about 30 times the distance to the sun
What was Plato's model of the universe?
The universe consists of crystalline spheres containing moon, sun, planets and stars (the celestial sphere)
Describe the motion of the planets in the sky.
-Generally, the planets move eastward through constellations
-Mars, Jupiter, Saturn, Uranus and Neptune move westward for some time when they rise in the east near the time of sunset (retrograde)
-Venus and Mercury alternate between eastward and westward motion; never get very far from sun in the sky
What is an epicycle and what did it explain?
A planet orbits around an invisible point (the deferent) which orbits the earth. It explained retrograde motion.
What was Ptolemy's model of the universe?
It modified Hipparchus' epicycle model
-Double epicycles
-Orbits' center not placed at earth
-planet's orbital speed not constant
-standard model for 1500 years
-predicted motions of planets, sun and moon well (not perfectly)
-not simple or symmetric
What are the 4 Layers of Plato's View of Reality?
1) Forms - True Concepts
2) Reasoning: hypotheses, math, geometry
3) Physical Objects
4) Images: views of objects, shadows
Describe Copernicus' model of the universe.
-heliocentric model proposed in "de Revolutionibus'
-still used circular orbits
-fixed stars
-retrograde motion: earth passes outer planets, inner planets pass earth
-added epicycles to try to match observed motions
How was Copernicus' model better/worse than Ptolemy's?
Better: correct about heliocentric; simpler and better explained retrograde motion

Worse: worse at predictions of planets' motion

*Leads to ambiguity in scientific method
Tycho Brahe
-great astronomer before telescopes
-measured distance to moon (triangulation)
-determined that comets and supernovas are more distant than moon (no parallax observed)
Johannes Kepler
-theoretical astronomer who used Tycho's data
-figured out that planets are in elliptical orbits around the sun (from Tycho's data on Mars' motion)
-Kepler's 3 Laws
Kepler's 1st law
A planet's orbit is an ellipse with the Sun at one focus
Kepler's 2nd law
An imaginary line between the sun and a planet sweeps out equal areas in equal time intervals
Kepler's 3rd law

Galileo Galilei
-used telescope
-studied motions of falling objects; found that all bodies fall at same rate
-discovered moon-like phases of Venus, which conflicts with geocentric model since then Venus could not have full or gibbous phase (always at angle <46 degrees from the sun)
-discovered 4 moons of Jupiter
-saw moon craters/mountains (not aether)
-saw sunspots (not perfect)
What are the implications of a heliocentric model?
-Earth is a planet like all the others
-Moon, planets, and sun made of substances found on earth (not aether)
-no distinction between celestial and terrestrial physical laws
-the universe is huge, possibly infinite
-Copernican Cosmological Principle: there's no special place in the universe
Distance equation
d=v(0)t + (1/2)at^2
Velocity equation
v=v(0) + at
Newton's 1st Law
Every body persists in its state of rest or of uniform motion unless it is compelled to change that state by forces impressed upon it. (related to inertia)
Newton's 2nd Law
The acceleration (a) of an object of mass (m) related to applied force (F) is:

F=ma or a=F/m
Newton's 3rd Law
Every action has an equal and opposite reaction
Conservation of momentum
If there is no net external force acting on an object or set of interacting objects, momentum is conserved
Newton's Law of Universal Gravitation
Kinetic Energy
Potential Energy
Newton's assumptions about space and time
space: unchanging structure in which objects are located

time: passage of time is steady and the same throughout the entire universe (einstein proved this is incorrect, but it is very close to correct if speeds are much less than light speed and gravity isn't super strong)
If system is complex (or slightly complex and enough time passes) outcome can be very sensitive to initial conditions or conditions at any other time
everything in the universe is determined by its initial conditions, even our own behavior