2. THE EARTH REVOLVES End of Chapter 1 Parts of Chapter 3

4. PLANETSPLANETS l The word, Planet, is derived from Planetes, the Greek word for Wanderer l Ancients recognized 7 wanderers (planets) l Today we understand that the Earth is a planet but not the Sun and Moon äSun, Moon, Mercury, Venus, Mars, Jupiter and Saturn äThe Sun is at the center of the solar system äThe Moon is a companion of Earth

5. RETROGRADE MOTION East West

6. RETROGRADE a la PTOLEMY Epicycle

8. SUN-CENTERED SYSTEM (1543)

9. RETROGRADE a la COPERNICUS Sun Planet’s Orbit Earth’sOrbit A A A B BB CCC DD D E EEW E

10. ORBITS of the PLANETS Inner Planets

11. ORBITS of the PLANETS Inner Planets Outer Planets

12. ORBITS of the PLANETS Ecliptic

13. A star rises  4 min earlier each night Stars drift westward about 1 º /day EARTH REVOLVES l Evidence that Earth Revolves around the Sun ä Changing Night Time Sky

14. SUMMER TRIANGLE

15. WINTER TRIANGLE MILKY WAY

16. FLASHCARDFLASHCARD WHY IS IT THAT STARS APPEAR TO RISE 4 MINUTES EARLIER EACH NIGHT? A) Earth moves eastward 360 degrees in 365 days – about 1 degree per day. So a star will appear to drift westward about 1 degree per day. 4 minutes is to 24 hours as 1 degree is to 360 degrees. B) 4 minutes is about the change in time due to the apparent motion of the Sun C) The Sun rises 4 minutes earlier each day during spring-summer. D) The Boulder, CO, Universal Time Signal is inaccurate and slips about 4 minutes per day.

17. WINTER TRIANGLE MILKY WAY

18. EARTH REVOLVES l Evidence that Earth Revolves around the Sun ä Changing Night Time Sky ä Parallactic Shift of Stars

19. SUN-CENTERED SYSTEM With a Sun-centered Solar System and a moving Earth, objects outside the Solar System can potentially exhibit parallax. Whether they do or not will depend on their distance. Tycho Brahe looked for parallax of the stars in the 1570’s as proof of the Copernican Theory. Did not see it - concluded that Earth did not move. Measurement accuracy 1’ whereas the parallax of nearest star < 1”.

20. PARALLAXPARALLAX

21. STELLAR PARALLAX

22. Bessel Measures Stellar Parallax 1838! 61 Cygni Parallax 0.314” Manhattan taxi as viewed from Mexico City Mexico City

23. EARTH REVOLVES l Evidence that Earth Revolves around the Sun ä Changing Night Time Sky ä Parallactic Shift of Stars ä Doppler Effect

31. WAVESWAVES l A stone dropped into a pool of water causes an expanding disturbance called a wave.

32. DOPPLER SHIFT

33. WAVESWAVES l Light and radio are waves (called electromagnetic radiation) caused by charged particles (mostly electrons) oscillating. l A stone dropped into a pool of water causes an expanding disturbance called a wave. l Sound is a wave caused by a pressure disturbance.

34. STELLAR DOPPLER SHIFT

35. DOPPLER SHIFT 1 2 34 2 1 4 3 Velocity Time

36. EARTH REVOLVES l Evidence that Earth Revolves around the Sun äChanging Night Time Sky äParallactic Shift of Stars äDoppler Effect äPhases of Venus

37. Galileo Galilei

38. Venus and Ptolemy

39. PHASES OF VENUS

41. EARTH REVOLVES l Evidence that Earth Revolves around the Sun äChanging Night Time Sky äParallactic Shift of Stars äDoppler Effect äPhases of Venus äMoons of Jupiter

42. MOONS OF JUPITER

43. Four Galilean moons of Jupiter as sketched by Galileo on 7 nights Between January 7 and 15, 1610