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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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Presentation Transcript
slide1

Chapter 2:

The Rise of Astronomy

early ideas pythagoras
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
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
slide13

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.
slide14

Aristotle’s model of a geo-centric solar system

(384-322 BC)

But model couldn’t account fully for retrograde motion of the planet!!!

ptolemy s geo centric solar system
Ptolemy’s Geo-centric Solar System

Tried to account

for retrograde

motion, but could

not quite

match

observations

slide17

Copernicus devised the first comprehensive helio-centric cosmology to successfully explain retrograde motion

slide20

Kepler’s First Law: The orbit of a planet about the Sun is an ellipse with the Sun at one focus.

slide21

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.

slide22

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.

slide23

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

slide24

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

slide27

Galileo’s telescope revealed all phases of Venus which could only occur IF Venus orbits the Sun.

geo centric or helio centric
Geo-centric or Helio-centric?

Galileo Ptolemy

Kepler Copernicus

Aristotle

slide29

Sir Isaac Newton

What goes up,

must come down!

slide31

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 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