chapter 2: the rise of astronomy. ancient roots: early homo-sapiens
TRANSCRIPT
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
• 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
But model couldn’t account fully for retrograde motion of the planet!!!
(384-322 BC)
Retrograde motion is the apparent “backward” motion of a planet
Ptolemy’s Geo-centric Solar System
Tried to accountfor retrogrademotion, but couldnot quite match observations
Copernicus devised the first comprehensive helio-centric cosmology to successfully explain retrograde motion
Tycho Brahe’s Golden Nose
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 .
Summary of Kepler’s Laws of Planetary Motion
The orbit of a planet about the Sun is an ellipse with the Sun at one focus
1st Law
The closer the planet is in its orbit around the Sun, the faster its speed is.
2nd
Law
The planets that are closest to the Sun orbit the Sun at a faster speed than planets that are farther away.
3rd
Law
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
What goes up, must come down!
Sir Isaac Newton
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
Foucault proves that the Earth rotates!