2. MOON & ECLIPSES

3. scale Drawn to scale: Earth Moon

4. Moon’s orbit – viewed from above Earth’s north pole  Orbit period = 27.3 days (Sidereal Period) Far side Near side

5. Near Side

6. Far Side

7. Diurnal (Daily) Motion: East to West, relative to horizon; rises & sets Monthly Motion: Eastward relative to stars; due to orbit of moon about Earth MOTION OF THE MOON (Viewed from Earth)

8. Orbit, viewed edge-on: Earth’s orbit plane Moon’s orbit plane 5o5o

9.  Orbits tipped  Orbit planes intersect along “Line of Nodes” * p. 41

10. Viewed from Earth, moon moves ~ 13 o /day E S W 9 pm 13 o

11. Does the moon rotate? eh?

14. The Lunar Phase Cycle E W p. 39

15. West Horizon toward sun Waxing Crescent

16. South Horizon First Quarter

17. South Horizon Waxing Gibbous

18. South Horizon Full

19. South Horizon Waning Gibbous

20. South Horizon Third (Last) Quarter

21. East Horizon Waning Crescent toward sun

22. Phase Movie Phase Movie E W

23. The Full Cycle 29.5 days – One ‘moonth’ p. 39

25. Sunlight  Just like Earth!  Phases result from viewing, from Earth, fractions of illuminated half.  Moon is always one-half illuminated. Understanding the Phase Cycle

26. Sunlight Note: Not to scale Earth Moon e.g., First Quarter View from Earth Result: Moon appears one-half illuminated

28. Phase Visibility

29. Eclipses Shadows > Umbra: Inner shadow > Penumbra: Outer shadow p. 41

30. Lunar Eclipses Moon moves through Earth’s shadow Require > Full Moon > Moon along nodal line The moon was as though drenched with blood. - The Anglo Saxon Chronicles (734 AD)

31. Note: not to scale The View from Space * Maximum duration of totality  100 min p. 42

32. The View from Earth Duration: 77 min

33. Partial Eclipse of July 28, 1999

34. Lunar eclipse occurs only when moon at/near nodal line No eclipse! Eclipse p. 41

35. From a vantage point in the plane of Earth’s orbit... Earth’s shadow misses moon  no eclipse! 5o5o

36. What explains the color? Sunlight Moon Earth Atmosphere  Atmosphere bends (refracts) sunlight into umbra  Atmosphere removes (scatters) blue/green part of light. Earth’s shadow

37. Eclipse of Jan 20 – 21, 2000 “... the moon drenched with blood.”

38. Solar Eclipses Earth intersects moon’s shadow Require > New Moon > Moon along nodal line Eclipse can be > Total > Partial > Annular And the moon in haste eclipsed her, and the Sun in anger swore He would curl his wick within him and give light to you no more. - Aristophanes, Chorus of Clouds (423 BC)

39. Basic Geometry of Solar Eclipse Umbra forms spot (diam ~ 100 mi) on Earth

40. Another View Spot moves generally eastward at ~ 1100 mi/hr, creating “zone of totality” Partial eclipse seen in penumbra p. 43

43. View from Earth: Sun, totally eclipsed. Solar Corona  Maximum duration of totality: ~7.5 minutes

44. Sun, partially eclipsed

45. Closest Farthest Moon’s orbit is not a circle...

46. Yielding Annular Eclipses: EarthMoonSun  Moon’s umbra does not reach Earth when moon too far away. p. 43

47. Ring or Annulus is seen when sun eclipsed. Farthest Closest Aug 24, 1998

48. Solar: about twice per year, somewhere on Earth. > At any given location, about once in 360 yrs. Lunar: about twice per year. How often do eclipses occur?

49. Total Solar Eclipses: 1997 - 2020 p. 44