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| Ages of the Earth and Universe |
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Earth: 4.5 billion yrs old Universe: 13.6 billion Why the gap? Successive steps |
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- Earth revolves around it's own 23.5 degree axis
- As it revolves the Northern and Southern Hemisphere receive more or less direct sunlight
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- the illusion that planets go backwards in motion
- this is caused due to Earth's faster rotational speed around the Sun
- helped challenge the idea of an Earth-centered universe
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- difference in direction of a celestial object as seen by the viewer
- Greeks could not detect it so they embraced a geocentric model
- nearer objects = greater parallax
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- the first to propose a geocentric model of the universe where Earth was at the center
- all celestial bodies were interconnected
- four basic elements: earth, air, fire, and water
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- supported the geocentric model
- concluded that all celestial bodies were NOT interconnected as Aristotle had proposed
- used epicycles in order to explain retrograde motion
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- pre-telescope observations
- given island and money from the government to execute his projects
- Believed Earth was at the center of the universe but every other planet revolved around the Sun
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- discovered that planets had an elliptical orbit around the sun
- Kepler's Laws
- orbital paths of planets are elliptical
- the closer a planet is to the Sun, the faster the orbit
- square of the planet's orbital period is proportional to the cube of it's semi-major axis
- Effects of his laws
- able to predict planet's position with greater accuracy
- anima motrix- the Sun has a force upon other planets
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- Copernican mode- the Sun is at the center of the universe
- Proposed that Earth revolved around it's own axis and the moon revolved around Earth
- explained retrograde motion and to some extent parallax
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- observations made in "The Starry Messenger"
- invented the telescope
- his observations helped give real evidence against the geocentric model
- deciphered that all objects fell at the same rate (g=9.8 m/s)
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Definition
- Laws of Motion
- Inertia-object will keep moving unless a forces acts upon it
- F=ma (force is equal to mass times acceleration)
- for every force there is always an equal reaction force
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- planets rise in the east and set in the west
- wander slowly through constellations
- motion varies in speed and brightness
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- Main Idea: Various ideas of how to find the circumference of the Earth
- Ptolemy's five arguments
- stars, moon, and sun don't rise the same time
- things occur earlier for west to east
- difference in local times
- north and south constellations don't appear in every hemisphere
- mountains seem to rise out of water
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- Galileo's groundbreaking observations
- Moon was not perfect
- Revolved around the Earth
- Jupiter
- Jupiter's moons revolved around Jupiter
- celestial bodies not revolving around earth
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Definition
Main Idea: The uses of waves in the electromagnetic spectrum in applications of astronomy |
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| Acceleration due to gravity |
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Definition
- acceleration of a falling object
- 9.8 m/s
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- Conservation of Momentum
- total momentum of interacting bodies cannot change unless an external force is applied
- Conservation of Angular Momentum
- as long as there is no twisting force, angular momentum cannot be changed
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- objects can gain or lose energy only by exchanging energy with other objects
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- equation: v=wavelength x frequency
- speed in vacuum is a constant
- types of waves
- transverse- light waves/stretched strings
- longitudinal- travels along direction the source vibrates
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- visible light is a very small component
- as wavelength increases, frequency decreases = lower energy
- EM waves- create a magnetic field which then produces an electrical field
- gamma rays are the shortest while radio waves are the longest
- unifying concept on light and sound
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Definition
- atoms contain electric potential energy stored in energy levels
- ground state- lowest possible energy level
- excited state- any other level
- when atoms bump to a higher level they are excited and unstable
- when they return to ground state the emit energy in the form of a photon
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- considered a chemical footprint of atoms
- used to determine composition and temperature of stars
- thermal radiation- tempature is determined by using thermal radiation
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- effect that shifts the wavelength of spectral features in moving objects
- blueshift- moving towards
- redshift- moving away
- use in astronomy
- tells the full motion of an object
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