Cosmology Midterm 1

Front 1

In science, what two things define beauty?

Back 1

Symmetry & Simplicity

Front 2

What were some of the uses of ancient cosmology?

Back 2

Calendars, navigation, religion, myths, astrology.

Front 3

What were some of the ancient calendar observatories?

Back 3

Stonehenge, the Great Pyramid of Giza, Chichen Itza, Bighorn Medicine Wheel

Front 4

How did the ancient Greeks determine that the moon is a sphere?

Back 4

Because the terminator (line separating the dark and light side of the moon) is curved

Front 5

Describe the ancient Greek view of the universe.

Back 5

It was geocentric - Earth was at the center and stationary.

Front 6

What reasons caused the Greeks to believe that the Earth was stationary?

Back 6

-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

Front 7

What were some of the incorrect assumptions of Ancient Greeks?

Back 7

-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

Front 8

What was Plato's model of the universe?

Back 8

The universe consists of crystalline spheres containing moon, sun, planets and stars (the celestial sphere)

Front 9

Describe the motion of the planets in the sky.

Back 9

-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

Front 10

What is an epicycle and what did it explain?

Back 10

A planet orbits around an invisible point (the deferent) which orbits the earth. It explained retrograde motion.

Front 11

What was Ptolemy's model of the universe?

Back 11

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

Front 12

What are the 4 Layers of Plato's View of Reality?

Back 12

1) Forms - True Concepts
2) Reasoning: hypotheses, math, geometry
3) Physical Objects
4) Images: views of objects, shadows

Front 13

Describe Copernicus' model of the universe.

Back 13

-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

Front 14

How was Copernicus' model better/worse than Ptolemy's?

Back 14

Better: correct about heliocentric; simpler and better explained retrograde motion

Worse: worse at predictions of planets' motion

*Leads to ambiguity in scientific method

Front 15

Tycho Brahe

Back 15

-great astronomer before telescopes
-measured distance to moon (triangulation)
-determined that comets and supernovas are more distant than moon (no parallax observed)

Front 16

Johannes Kepler

Back 16

-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
-

Front 17

Kepler's 1st law

Back 17

A planet's orbit is an ellipse with the Sun at one focus

Front 18

Kepler's 2nd law

Back 18

An imaginary line between the sun and a planet sweeps out equal areas in equal time intervals

Front 19

Kepler's 3rd law

Back 19

P^2=A^3

P^2=(A^3)/M

Front 20

Galileo Galilei

Back 20

-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)

Front 21

What are the implications of a heliocentric model?

Back 21

-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

Front 22

Distance equation

Back 22

d=v(0)t + (1/2)at^2

Front 23

Velocity equation

Back 23

v=v(0) + at

Front 24

Newton's 1st Law

Back 24

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)

Front 25

Newton's 2nd Law

Back 25

The acceleration (a) of an object of mass (m) related to applied force (F) is:

F=ma or a=F/m

Front 26

Newton's 3rd Law

Back 26

Every action has an equal and opposite reaction

Front 27

Momentum

Back 27

p=mv

Front 28

Conservation of momentum

Back 28

If there is no net external force acting on an object or set of interacting objects, momentum is conserved

Front 29

Newton's Law of Universal Gravitation

Back 29

F=-(GMm)/r^2

Front 30

Kinetic Energy

Back 30

KE=(1/2)mv^2

Front 31

Potential Energy

Back 31

PE=mgh

Front 32

Newton's assumptions about space and time

Back 32

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)

Front 33

Chaos

Back 33

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

Front 34

Determinism

Back 34

everything in the universe is determined by its initial conditions, even our own behavior