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Chapter 2: The Rise of Astronomy. Ancient Roots: Early Homo-Sapiens. Ancient Roots: Egyptian. Ancient Roots: England. Ancient Roots: Mayan. Ancient Roots: Aztec. Ancient Roots: Incan. Ancient Roots: Cambodia. Ancient Roots: Anasazi. Early Ideas: Pythagoras.
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Chapter 2: The Rise of Astronomy
Early Ideas: Pythagoras • Pythagoras in 500 B.C. taught that the Earth was round based on the belief that the sphere is the perfect shape used by the gods
Early Ideas: Aristotle • By 300 B.C., Aristotle presented naked-eye observations for the Earth’s spherical shape: • Shape of Earth’s shadow on the Moon during an eclipse
The Hot Debate! • A geo-centric cosmology is a theory that proposes Earth to be at the center of the universe. • versus • A helio-centric cosmology is a theory that proposes the Sun to be at the center of the universe.
Aristotle’s model of a geo-centric solar system (384-322 BC) But model couldn’t account fully for retrograde motion of the planet!!!
Retrograde motionis the apparent “backward” motion of a planet
Ptolemy’s Geo-centric Solar System Tried to account for retrograde motion, but could not quite match observations
Copernicus devised the first comprehensive helio-centric cosmology to successfully explain retrograde motion
Mathematician Johannes Kepler created laws of planetary motion
Kepler’s First Law: The orbit of a planet about the Sun is an ellipse with the Sun at one focus.
Kepler’s Second Law: A line joining a planet and the Sun sweeps out equal areas in equal intervals of time. In other words, the closer a planet is in its orbit around the Sun, the faster its speed is.
Kepler’s Third Law In other words, the planets that are closest to the Sun orbit the Sun at a faster speed than planets that are farther away.
The orbit of a planet about the Sun is an ellipse with the Sun at one focus 1st Law 2nd Law The closer the planet is in its orbit around the Sun, the faster its speed is. The planets that are closest to the Sun orbit the Sun at a faster speed than planets that are farther away. 3rd Law Summary of Kepler’s Laws of Planetary Motion
Italian scientist Galileo made discoveries that strongly supported a helio-centric cosmology “I do not feel obliged to believe that the samegod who has endowed us with sense, reason andintellect has intended us to forgo their use.” - Galileo
Galileo’s telescope revealed that Jupiter had moons which orbited Jupiter instead of Earth.
Galileo’s telescope revealed all phases of Venus which could only occur IF Venus orbits the Sun.
Geo-centric or Helio-centric? Galileo Ptolemy Kepler Copernicus Aristotle
Sir Isaac Newton What goes up, must come down!
Newton’s Universal Law of Gravitation • Every body that has mass has gravity • The gravity between the two bodies increase with the mass • The gravity between the two bodies increase if they are closer together.
Mass vs. Weight • Mass is a measure of the total amount of material in the object remains the same everywhere • Weight is the force with which an object is pulled down while on the ground (due to gravity’s attraction) changes depending on the body you are standing on
