Lesson 3 Flashcards
Ancient time tellers
- sun’s pattern through sky
- sundials
- egyptians = huge obelisks
- Water clocks
Marking seasons
- ancient cultures built structures to help mark seasons
- Stonehenge
- Templo Mayar
- Sun dagger, New Mexico; single dagger pointed to noon on summer solstice, but two daggers surrounded in winter solstice
Archaeastronomy
- piece together astronomical achievements of the past based on physical evidence left behind
Ancient navigation
- Polynesian Navigators used astronomy for wave and swell patterns
Three philosophical innovations
- tradition of trying to understand nature without relying on supernatural
- Math to give precision to ideas
- power of reasoning from observations
Scientific Model
- conceptual representation created to explain and predict observed phenomena
History of Libraries
Started with Alexander the Great’s library, but that burnt down –> knowledge moved to Baghdad
Greek geocentric model
- Earth is centre of universe
- Thales started questioning things
- Anaximander; celestial sphere
- Pythagoras; Earth is perfect sphere
- Plato: objects move in perfect circles at constant speeds around Earth (but retrograde motion?)
- Eudoxus; sun, moon and planets each have own spheres nested within several other spheres
- Aristotle: earth is centre and gravity pulled heavy things toward centre creating earth (geocentric model then stayed because him)
Ptolemy’s model
- Earth centre
- each planet moves around a small circle that turns upon larger circle to explain retrograde motion
Copernican Revolution
- Copernicus: Geocentric was too complex to explain retrograde motion so tried Sun-centered (first applied by Aristarchus)
- But didn’t let go of perfect circles, so very complex
- Tycho Brahe:
because of lack of parallax, concluded sun orbits earth while all other planets orbit the sun - Kepler: planetary orbits are ellipses
Ellipse
- oval shaped
- Semimajor axis is half of long end
- perihelion is closer to one end where sun lies
Eccentricity
- how much an ellipse is spread out
Kepler’s 3 laws
1) Orbit of each planet about the Sun is an ellipse with the Sun at one focus (closest point perihelion, farthest is aphelion)
2) Planets move faster in the part of its orbit nearer the Sun and slower when farther from the Sun
3) More distant planets orbit the Sun at slower average speeds (p^2 = a^3)
How did Galileo solidify Copernican Revolution?
- moving objects remained in motion unless force acts to stop it (therefore Aristotle’s idea that if Earth was moving birds would be left behind)
- Used telescope to show that celestial things weren’t perfect like people thought therefore it’s okay if it isn’t circular
- Showed that stars were actually SUPER far therefore explained why stellar parallax wasn’t visible
- observed Jupiter’s 4 moons orbiting Jupiter NOT Earth
