Chapter 3 Flashcards
Geocentric Model
Earth-centric
Who was one of the first prominent proponents of the geocentric model?
Claudius Ptolemaeus 90-168 CE
Prograde Motion
Eastward Motion
Retrograde Motion
Planets appear to move westward for a time before resuming their normal eastward direction
Why did early astronomers believe the geocentric model?
1) We couldn’t feel earth’s rotation around the sun.
2) Various religious believes reinforced mankind sense that the world was made for them or they were the highest form of life.
Epicycle
A small circle superimposed on each plant to explain retrograde motion.
What are the three major assumptions of early astronomers?
- The earth is the center of the solar system.
- The planets and sun orbited in uniform circles.
- Objects in space are made up of a different substance than the earth.
Heliocentric Model
Planets are orbiting the sun including earth.
What assumptions did Copernicus dispel of in his model.
- the earth is the center of the solar system.
2. Objects in space are made up of a different substance than the earth.
What did Copernicus still include in his model?
1) Epicycles (althought they were greatly reduced
2) The planets and sun orbited in uniform circles.
What was a major element that was missing from Copernicus’ work?
He had no proof that his model was correct other than it being mathematically more simplistic.
Empirical Science
Based on observational data which seeks to describe patterns.
Tycho Brahe
Studied law before seeing a solar ecclipse. Granted an island by the king. Hired a mathwiz Kepler as his intern to confirm if his model was true. Made detailed notes of positions of planets over several years using protractors.
Geo-Heliocentric Frame
Tycho’s solution between the Heliocentric and Geocentric Model. The planets orbited the sun and the sun and planets orbited the earth.
Johannes Kepler
Mathematician who was a proponent of the Copernican Model. Corrected Tycho’s model and further proved the Copernican model was correct. Derived three laws to describe planetary motion.
Kepler’s First Law
Planets orbit in ellipses with the sun at one of the two foci. Eccentricity is = distrance from the center of focus/semimajor axis
How do you calculate eccentricity
E= Distance from the center of focus/ semimajor axis
Kepler’s Second Law
A line between the planets and sun sweeps out in equal areas in equal time. Orbit at perihelion must be faster to cover the same area as the aphelion.
Perihelion
Point in orbit closest to sun
Aphelion
Point in orbit furthest away from the sun.
Kepler’s Third Law
Period of the planet squared=semimajor axis of orbit cubed. For all planets a3/p2=1
Using Halley’s Comet’s Period of 76 years calculate the semimajor axis of its orbit.
17.94 au. 76^3=a3
Galileo
First astronomer to use a telescope to observe and report significant objects
What were Galileo two biggest discoveries?
1) Moons around Jupiter.
2) Phases of Venus
What did Galileo observe when he looked at the moons of Jupiter?
1) Originally thought they were moons
2) Observed Jupiter remained relative in the same spot but the moons moved.
3) Observed moons would disappear and reappear
4) Deduced that they must be moons in orbit around Jupiter.
What were the scientific consequences of Galileo’s discovery that Jupiter had moons?
1) Good observational evidence that other planets have moons just like earth.
2) Our planet is not unique.
3) More arguments for the Heliocentric model.
What did Galileo observe when looking at Venus in a telescope?
Observed phases similar to that of the moon?
How did the Heliocentric model fit the observational data of Galileo vs the Geocentric model for the phases of Venus?
In the Geocentric Model, one would predict that the full venus phases would not be visible because of its proximity to the sun. But in the Heliocentric model one would predict phases similar to that of the moon.
What was important about Galileo’s observations about the phases of Venus?
- Actual evidence that the planets orbit the sun rather than the earth.
- Venus is closer to the sun that earth.
What was the most likely reason Galileo was placed under house arrest?
Wrote “Dialogue on the Two World Systems” in 1632. In which two philosophers and a layperson discuss the two competing models. The lay person “Simplicio” made arguments which closely resemble that of the pope.
Sir Isaac Newton
1) Invented Calculus at the age of 23.
2) Proposed three laws that explain planetary motion.
3) Founder of classical mechanics.
Newton’s Laws
1) Law of Inertia. An object in motion or at rest will remain in motion or rest unless acted upon by another force.
2) F=MA Force causes motion
3) Equal and Oppisite. For every force there is an equal and opposite force.
Newton
kgms^-2=kgm/s^2
Force
A push or a pull. Causes an object to accelerate.
Gravitational Force
Objects experience an acceleration due to gravity. Equal to 9.8m/s2 on earth Acceleration due to gravity points to the center of earth.
Where is gravity weakest and strongest on earth
Weakest on the equator and strongest at the poles because there is less distance to the center of earth.
What did Galileo Observe about falling objects?
Observed that objects of different masses fall at the same rate.
What does gravitational force depend on?
1) The mass of the objects
2) The distance between the objects.
Newton’s Law of Gravity
Fgrav=Gx (m1*m2)/r^2 G is the universal gravitational constant of 6.67 * 10^-11
