22.1 Early Astronomy

Ancient Greeks• Astronomy is the science that studies the

universe

• Deals with properties of objects in space & the

laws under which the universe operates

• Aristotle – Earth is round bc it always casts a

curved shadow when it passes btw the sun &

moon

• Eratosthenes – established the size of Earth

• Hipparchus – star catalog

Geocentric Model• Earth was a sphere that stayed motionless

at the center of the universe

• The moon, sun, & the known planets –

Mercury, Venus, Mars, & Jupiter – orbit Earth

• Beyond the planets were hollow space, this

is were the stars traveled daily around the

Earth

• Not a correct model

Heliocentric Model

• Sun centered model

• Aristarchus was the 1st to believe this model

• Earth & other planets orbit the sun

• Although there was evidence for this model,

the Earth centered model dominated

Western thoughts for about 2000 yrs

Ptolemaic System

• Claudius Ptolemy

• Presented a model of the universe

• Accounted for the movements of the

planets

• Retrograde Motion results in a

combination of the motion of Earth &

the planet’s own motion around the sun

The Birth of Modern Astronomy

• Nicolaus Copernicus

• Tycho Brahe

• Johannes Kepler

• Galileo Galillei

• Sir Isaac Newton

Nicolaus Copernicus• From Poland

• Convinced that Earth is a planet just like the

other five that were known

• Daily motions of the heavens could be better

explained by a rotating Earth

• Changed the model of the solar system to

having the sun at the center & the planets

(Mercury, Venus, Earth, Mars, Jupiter, & Saturn)

orbiting around it

Tycho Brahe• Born 3 years after the death of Copernicus

• Designed & built instruments called pointers

which were used for 20 yrs to measure the

locations of the heavenly bodies

• Brahe’s observations, esp. of Mars, were far

more precise than any that were previously

made

• Johannes Kepler was his assistant

Johannes Kepler

• Discovered 3 laws of planetary motion (pg.

618)

• Discovered that the orbit of Mars around the

sun was an oval shaped path = eclipse

• Mars approaches the sun = speeds up

• Mars moves away from the sun = slows down

Galileo Galilei

• Descriptions of the behavior of moving objects

• Constructed his own telescope

• Discovery of 4 satellites or moons orbiting Jupiter

• Discovery that the planets are circular disks

• Discovery that Venus has phases just like the moon

• Discovery that the moon’s surface was not smooth

• Discovery that the sun had sunspots, or dark

regions

Sir Isaac Newton

• Was the 1st to formulate & test the law of

universal gravitation

• Inertia

• Gravitational force decreases w/ distance

• Greater the mass of the object, the

greater its gravitational force

REVIEW REVIEW REVIEWLocation of Earth

Location of Sun

Supporters of Model

Geocentric Model

Center of Universe

________________ ________________

Heliocentric Model

________________ Center of Universe

Aristarchus, Copernicus

• What produces the retrograde motion of Mars?

• What major change did Copernicus make in the Ptolemaic system? Why was this change so significant?

• In your own words summarize Kepler’s 3 lays of planetary motion.