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 REVIEW What produces the retrograde motion of Mars? Location of Earth Location of Sun Supporters of Model Geocentric Model Center of Universe ________________ Heliocentric Model 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.