Study Guide 1

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 Astronomy 105
 Study Guide - Exam 1
 
 
Notice how these important discoveries influenced the world 
model in use at the time.
 
People Discovery Model (Philosophy)
 
Ancient Day-night corresponds to Flat earth, spherical
 sky with position of sun sun attached, turning
 in the sky. above fixed earth
 
Ancient Rise and set points of Sun not moving like a star
 sun related to change of Predictions of plant-
 seasons. ing times feasible
 
Babylonians Plotting sun's position Nature's predict-
 on star charts. Relating ability. Infinite
 sun's position among time scale. Ritual
 stars with rise point. and religion con-
 Finding paths of moon nected with sky.
 and planets close to Fatalistic predeter-
 and on the ecliptic. minism
 Retrograde motion of the
 planets.
 
Greeks Phases of moon explained. 3-D universe needed
 Eclipses successfully Sun farther away than
 predicted. moon. Moon is dark.
 
Greeks Shadow of earth during  Earth is spherical
 lunar eclipse circular.
Greeks Sizes, distances of sun, All observations
 moon. Size of earth. until now formalized
 in geocentric model
 
350 B.C. Aristotle - Geocentric Model
 1. Earth stationery center of the universe
 2. Sun, moon, planets on separate spheres
 revolving about the earth.
 3. Stars on one sphere at edge of universe.
 4. All motions on circles.
 5. Separation of Celestial from Terrestrial
 Realm.
 
140 A.D. Revision of Ptolemy to account for retrograde
 motions.
 1. Planets move on epicycle.
 2. Center of epicycle moves on deferent.
 3. Earth may be offset from center of deferent.
 4. Adjust sizes and speeds to match observations.
 
Arguments for stationery Earth (caution – lots of erroneous thinking here)
 1. No apparent motion.
 2. Earth is heavy - celestial objects unknown.
 Easier to imagine them moving rather than heavy
 earth.
 3. No parallax observed.
 4. If earth moved, wouldn't everything fly off?
 5. Force required for motion - no force can be
  detected acting on the earth.
 
The Astronomical Revolution - The Heliocentric Model
 
Know these planetary configurations. Where and when would we
look for planets in these configurations in the sky?
 
 Inferior Planets Superior Planets
 
 Inferior conjunction Conjunction
 Superior conjunction Opposition
 Greatest western elongation Western Quadrature
 Greatest eastern elongation Eastern Quadrature
 
Ex. When can a superior planet transit (cross the Celestial
 Meridian) at midnight?
 
Ans. First you need to know what midnight is. Midnight
 occurs when the sun crossed the celestial meridian
 below the horizon. (This is also called lower
 culmination). For the planet to be transiting then,
 it must be on the other side of the sky from the sun
 or at opposition.
 
Ex. What phase is Venus in at inferior conjunction?
 
Ans. New
 
Other planetary motion terms.
 sidereal period ellipse astronomical unit
 synodic period focus perihelion
 semi-minor axis semi-major axis aphelion
 
Kepler's Laws
 
 1. All planets orbit the sun in ellipses, the sun
 being at one focus of the ellipse.
 2. A line connecting the sun with a planet sweeps out
 equal areas in equal intervals of time.
 3. The sidereal period of a planet squared in
 proportional to the length of its semi-major axis
 cubed.
 
 Consequences:
 Law 2 says that a planet moves faster near perihelion
 Law 3 says that P² = a³ for the solar system where we
 measure period in years and semi-major axis in a.u.
 
Contributions of the key figures of Renaissance Astronomy
 
Copernicus removed man from the center of the universe.
 Gave method of determining planetary distances
 for the first time.
 
Tycho Brahe realized that only precision observations could
 prove or disprove any world model.
 
Kepler gave empirical laws of planetary motion based
 on observations of Tycho. Realized that in
 discerning truth, observations should take
 precedence over theory. Theories should
 conform to observations.
 
Galileo first to begin formulating laws of general
 motion. Used telescope to refute Aristilean
 view. Saw in his experiments and telescopic
 observations that one set of laws can describe
 motions everywhere in the universe.
 
Newton generalized laws of motion. Unified all
 motions in the universe under one set of laws.
 This is sometimes referred to as the Newtonian
 Synthesis.
 
Galileo's Observations
 1. Moon - imperfect, earth like, dark body
 2. Jupiter - had moons. Not everything went around
 earth.
 3. Venus - went through phases not predicted by the
 geocentric model.
 
 Generally showed that Aristotle could be wrong on some
 points so why not on others.
 
Newton's Laws
 1. In the absence of external forces, an object will
 continue its previous motion.
 2. Sum of Forces = ma
 3. For every action there exists an equal and opposite
  reaction.
 
Universal Law of Gravitation
 mass causes gravity
 gravity acts at a distance
 with gravity and the three laws, Kepler's Laws were
 mathematically proven