1. Eclipses and Tides: Sun/Earth/Moon Relationships

2. Eclipse: When the shadow of one object falls on another
When Earth’s shadow covers Moon
When the Moon’s shadow falls on Earth

3. Solar Eclipse:
Occurs when moon passes between the earth and the sun

4. Video: Annular Sun Eclipse (Solar Eclipse)

5. Question:
What are the relative positions of the earth, moon and sun during an eclipse?

6. Solar Eclipse: Moon blocks sunlight from reaching Earth
Moon’s shadow falls on Earth

7. Solar Eclipse:
Happens during New Moon because lighted side of moon is facing away from earth

8. Question:
Why do eclipses NOT happen every month?

9. Solar Eclipse: Does not happen with every New Moon
Moon’s orbit is tilted 5o from earth’s orbit
Moon rarely goes between sun and earth

10. Total Solar Eclipse:

11. Total Solar Eclipse: Occurs where the Umbra hits Earth
Umbra: darkest part of shadow
Cone shaped

12. Total Solar Eclipse:

13. Total Solar Eclipse: Only small part of earth gets total solar eclipse
Solar corona can be seen
Sky is dark and stars can be seen

14. Partial Solar Eclipse:
Some sun is visible
Partial shadow, called Penumbra, falls on earth

15. Partial Solar Eclipse:

16. Partial Solar Eclipse:
Sky is darker but not like night

17. Partial Solar Eclipse:
Few stars can be seen
Dangerous to look at partial eclipse

18. Question:
What are the relative positions of the earth, moon and sun during a lunar eclipse?

19. Lunar eclipse: Occurs at full moon
Earth is directly between sun and moon
Earth’s shadow passes over face of moon

20. Video: Lunar Eclipse 12-20-2010

21. Total Lunar Eclipse:
Earth’s umbra passes over Moon

22. Total Lunar Eclipse:
Moon goes darker as it passes into earth’s shadow

23. Total Lunar Eclipse:
Appears red when total eclipse occurs

24. Partial Lunar Eclipse:
Occurs when sun, earth and moon are not quite in line
Only part of moon is in earth’s umbra

25. Partial Lunar Eclipse:
Edge of shadow is blurred
This is penumbra

26. Video: Watch Lunar Eclipse 2010

27. Answer these in your notes:
Why do solar eclipses not happen every month?
Why do solar eclipses only happen at new moon?
Why do lunar eclipses not happen every month?
Why do lunar eclipses only happen during a full moon?

28. Question:
How does gravity cause tides?

29. Tides The rising and falling of water levels on a 12.5 hour cycle
Caused by gravity and inertia

32. This means that the sun, moon and earth all pull on each other

36. How this causes tides:

37. Video: Tides

38. Moon pulls earth’s water to a point closer to the moon
The water is freer to move
Causes a bulge, or high tide

39. Moon’s gravity also pulls on Earth
The water on the opposite side of earth from the moon resists the pull – inertia
Creates another bulge, or high tide, on opposite side of earth

41. Low tides: Occur between the high tides In time Geographically
See figure 10, page 33

42. Tide Cycle: 25 hours High tides every 12.5 hours
Low tides follow high tides about every 6 hours

43. Spring tides:
The sun also pulls on the earth and its water

44. Spring tides: Twice a month. The sun, moon and earth line up New moon
Full moon

45. Spring tides:
Combines the gravitational forces of the sun and the moon on the water

46. Spring tides:
Creates highest tides with greatest difference between high and low tides

47. Neap tides:
Twice a month, sun and moon are at 90o angle from each other
First and third quarter

48. Neap tides: Sun pulls water in different direction
Least difference between high and low tides