1. Know about the Celestial Sphere Know about the Greek Earth- Centered Model Know about Ptolemy’s Model. Prehistoric and Classical Astronomy

3. Overview Prehistoric and Classical Astronomy Astronomy and the Renaissance The Enlightenment and Modern Astronomy

4. The Celestial Sphere Celestial sphere refers to an imaginary sphere of heavenly objects that seems to center on the observer North Celestial Pole South Celestial Pole Constellation

5. The Celestial Sphere

6. It takes the Sun about 365.25 days to revolve around the celestial sphere The ecliptic is the name for the Sun’s apparent path among the stars around the Earth The zodiac is the group of constellations the Sun passes through on its apparent path along the ecliptic

7. The Moon’s Phases The Moon does orbit the Earth Earth’s gravity holds the Moon in such a firm grip that it always keeps the same face turned toward the Earth

8. The Moon’s Phases: Class Activity WAX = On WAIN = Off Crescent First Quarter GibbousFull Crescent Gibbous Third Quarter 1) Identify the phase 2) Waxing or Waning?

9. Observing Planetary Motion Retrograde Motion Planets move in elliptical, not circular orbits Revolve around the Sun, not Earth

10. The Greek Earth-Centered Model Thales of Mileus (600 BC) Stars are not gods Pythagoras (530 BC) Spherical Earth Aristotle (322 BC) Placed the Earth at the center of things

11. Ptolemy’s Model Claudius Ptolemy – AD 150 Ptolemy believed that heavenly bodies (planets and stars) were perfect, in contrast to earthbound objects For 1,300 years, his model was the conventional wisdom of the scientific world The universe was based on perfect circles An epicycle is the circular orbit of a planet, the center of which revolves around the Earth in another circle

12. Evaluating Ptolemy’s Model Strengths Fits evidence available during his lifetime Includes testable predictions Weaknesses Assumed that Earth was stationary Theory of epicycles was a departure from simplicity and symmetry

14. Next… Done – Prehistoric and Classical Astronomy Next – Astronomy and the Renaissance

15. Know about the Celestial Sphere Know about the Greek Earth- Centered Model Know about Ptolemy’s Model. Prehistoric and Classical Astronomy