StudyGuide1.pdf PHYS 104-01
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Popular in Astronomy
This 2 page Study Guide was uploaded by Sophie Stella on Wednesday February 24, 2016. The Study Guide belongs to PHYS 104-01 at University of St. Thomas taught by Dr. Ruch in Winter 2016. Since its upload, it has received 188 views. For similar materials see Astronomy in Astronomy at University of St. Thomas.
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Date Created: 02/24/16
PHYS 104: Astronomy Study Guide for the first Exam: 2/26/16 Definitions Celestial Sphere: The apparent sphere surrounding Earth upon which all celestial objects appear. Zenith: The point on the celestial sphere directly overhead. Meridian: An imaginary line running from North to South through the Zenith. Celestial Equator: A projection of the Earth's equator onto the celestial sphere. Celestial Hemisphere: The half of the sphere one can see from one's vantage point. The Ecliptic: The apparent path of the sun against the background stars over the course of a year. Solar Day: The amount of time it takes the sun to return to meridian. Sidereal Day: The amount of time it takes a background star to return to meridian. 1 A.U. (Astronomical Unit): The distance from the Earth to the sun. Perihelion: The closest point to the sun on an elliptical orbit. Aphelion: The furthest point from the sun on an elliptical orbit. Scientific Hypothesis: A conjecture that must be falsifiable in order to be valid. Scientific Theory: A hypothesis shown to be valid by experimental evidence. Epicycle: The retrograde motion of a planet orbiting something else when viewed on Earth. Geocentric: Having Earth at the center. Heliocentric: Having the sun at the center. Orbital Period: The amount of time required to complete one orbit. Longer period for larger orbits. Orbital Velocity: The speed of the planet in orbit. Emperical: Not based on an assumption on how the universe works. Inertia: A massive object's tendency to resist change. Force: A push or pull resulting in the movement of an object and acceleration. Forces cause an acceleration Position: Where an object is with respect to some reference. Uses coordinates. Velocity: The rate in which the position is changing. A change in direction counts as a change in velocity. Acceleration: The rate in which the velocity is changing. Astronomers Aristotle • According to Aristotle, each celestial object is embedded in a crystal sphere. • Each sphere rotates around Earth at a fixed rate. This wasn't able to explain retrograde motion. Ptolomy • Created the first model including epicycles Heliocentric model with epicycles Nicholas Copernicus • Created the first heliocentric model ◦ A simple solution to the retrograde motion of planets ◦ Has simple orbital period calculations ◦ This model was no more accurate than Ptolomey's Tycho Brahe • Took 2 decades worth of naked eye planet observations. • His new model had accuracy to within one minute arc. Johannes Kepler • A student of Tycho, who studied his data. • Discovered three empirical relationships. • Trusted Copernicus' model. nd • Suggested that the sun exerts a force on the planets. 2 Law:A line joining a planet and the sun sweeps out equal areas during equal intervals of time. (Fast at perihelion, slow at aphelion.) Distance traveled = Velocity x Time rd 3 Law: P²=a³ where P is the orbital period and a is the semi-major axis. Isaac Newton • Three laws of motion • Universal Gravitation • Calculus Simple central principles from which all motion can be derived. st 1ndaw: Left on their own, massive bodies have a constant velocity. 2 Law: Forces cause a change in velocity. F=ma 3 Law: If you apply a force to something, it pushes back. Universal Law of Gravitation: Objects with mass exert an attractive force on one another. What do we see from Earth and why? The visibility of the celestial sphere changes with respect to one's position on earth. Earth is a sphere. We are on the Earth's surface. Earth spins around its axis one time per day. The sphere orbits the sun one time per year. Earth's axis of rotation is tilted with respect to the sun and Earth's orbit. Other planets orbit the sun in the same plane. The North Star – A star which the north axis of Earth points directly towards. – This star is at zenith at the north pole.
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