2. Astronomy The Science that Studies The Universe Ancient Greeks To Isaac Newton

3. Geocentric Model of the Universe Aristotle 384 BC -1600’s AD The Moon, the Sun and the Planets (Mercury, Venus, Mars, Jupiter and Saturn) go around Earth within a hollow celestial sphere of Stars

4. Heliocentric Model of the Universe 312 BC to Present Sun centered universe with the Earth and the other planets orbiting the Sun

5. Ptolemaic System (AD141) Planets move in circles about the Earth Planets also moved in tiny circles in their orbit, which were called epicycles The epicycles explained an apparent backwards motion of the planets against the stars called “retrograde”

6. The Birth of Modern Astronomy Nicolaus Copernicus (1500 AD) concluded Earth is a planet and the Sun is at the center of its motionNicolaus Copernicus (1500 AD) concluded Earth is a planet and the Sun is at the center of its motion

7. Tycho Brahe 1600 AD Built an observatory in Denmark Constructed the most precise astronomical measuring devices of his time that measured the angles of the stars and planets

8. Johannes Kepler 1600 AD An assistant to Tycho Brahe Used Tycho’s observations to develop his three laws of planetary motion: 1. Each planet travels in an ellipse about the Sun 2. Every month a line drawn from the Sun to a planet would “sweep out” the same area 3. There is a single mathematical relationship for all the planets traveling around the Sun, describing the length of time to get around (orbital period) relative to how far they were from the Sun (the further out the longer to get around)

9. Galileo Galilei 1600 AD His most important contributions were his descriptions of the behavior of moving objects.His most important contributions were his descriptions of the behavior of moving objects. With his telescope he discovered :With his telescope he discovered : four moons orbiting Jupiter four moons orbiting Jupiter planets are not just points of light like stars planets are not just points of light like stars Venus has “phases” like our Moon Venus has “phases” like our Moon the Moon’s surface was not smooth the Moon’s surface was not smooth the sun had sunspots the sun had sunspots

10. Sir Isaac Newton 1700 AD He developed the concept of universal gravitation: every body in the universe attracts every other body with a force that depends on the mass of each and the distance of separation Two times the mass = Twice the forceTwo times the mass = Twice the force Two times the distance = 1/4 th the forceTwo times the distance = 1/4 th the force Three times the distance = 1/9 th the forceThree times the distance = 1/9 th the force He explained the reasons for Kepler’s laws He explained the reasons for Kepler’s laws

11. Summary & Review use these question to guide you in writing your summary 1.Which model of the structure of the universe did Copernicus use? 2.List three of Galileo’s contributions. 3.Which law did Isaac Newton give to us?