1. Geometry: Sun – Moon– Earth
Eclipses
Eclipses are named after the object that “disappears”
Lunar eclipse:
Moon “disappears”
Geometry: Sun – Earth – Moon
Solar eclipse:
Sun “disappears”
Geometry: Sun – Moon– Earth

2. Lunar Eclipses
Lunar eclipses occur when the Moon enters the shadow of the Earth
The Earth’s shadow has 2 parts:
Umbra – all sunlight blocked
Penumbra – only some sunlight blocked
3 types of lunar eclipses:
Total – all of Moon in umbra
Partial – only part of Moon in umbra
Penumbral – Moon only in penumbra

3. TPS Question Who can see Lunar Eclipses? Anyone on Earth’s day side
Anyone on Earth’s night side
Anyone near the Earth’s equator
Anyone at all

4. Anatomy of a Lunar Eclipse

5. Lunar Eclipse

6. Solar Eclipses
Solar eclipses occur when the Earth enters the shadow of the Moon (the Moon blocks the Sun).
Moon and the Sun have approximately the same (apparent) angular size (1/2 degree).
Sometimes the Moon doesn’t cover the whole Sun and we get an annular eclipse.

7. The Moon’s shadow also has 2 parts:
Umbra – all sunlight blocked
Penumbra – only some sunlight blocked
3 types of lunar eclipses:
Total – Sun completely covered by Moon
Partial – Only part of the Sun covered by Moon
Annular – Some sunlight gets around edge of Moon

8. TPS Question Who can see total Solar Eclipses?
Anyone on Earth’s night side
Anyone on Earth’s day side
Anyone near the Earth’s equator
Only people along a certain path

9. Anatomy of a Solar Eclipse

10. Solar Eclipse
Moon is between Earth and Sun

11. Solar Eclipses
Solar eclipse is partial when only part of Sun is blocked, total when it all is, and annular when Moon is too far from Earth for total

13. Solar Eclipse Movie

15. Eclipse Frequency
Why isn’t there a lunar eclipse during every full moon?
Why isn’t there a solar eclipse during every new moon?
Because the Moon’s orbit around the Earth is tilted.

16. The Line of Nodes
Do an in-class demo.

17. When the Moon is in the plane of the ecliptic, eclipses can occur.
New Moon – Solar Eclipse
Full Moon – Lunar Eclipse

18. When the Moon is off the plane of the ecliptic, no eclipses can occur.
New Moon, but no Solar Eclipse
Full Moon, but no Lunar Eclipse

19. Eclipse Frequency
Eclipses don’t occur every month because Earth’s and Moon’s orbits are not in the same plane

20. Number of eclipses per year:
Solar – at least 2, no more than 5
Lunar – maximum is 3
Combined -- maximum is 7
Maximum duration of eclipses:
Solar – 7 ½ minutes
Lunar – 1 hour, 47 minutes

21. Eclipse tracks,

22. Tides
Gravity: The Moon pulls more on the near side of the Earth than the far side.

23. Tides
As a result, water in the oceans is at “high tide” twice a day. Once on the near side to the Moon and again on the far side from the Moon.

24. TPS Question
new moon
full moon
third quarter moon
both new and full moon
At what lunar phase would the variation between high & low tides be greatest?

25. TPS Question
new moon
full moon
third quarter moon
both new and full moon
At what lunar phase would the tidal variation be greatest?
At new & full moon phases, the Sun and Moon combine to stretch the Earth and its oceans even more. We see higher high tides and lower low tides.

26. Spring and Neap Tides
The Sun can also cause tides, but only half as strong as the Moon.
Spring tide – when the tides from the Sun and the Moon combine
Neap tide – when the tides from the Sun and the Moon counter-act each other.

27. Spring and Neap Tides
The Sun has less effect, but it does modify the lunar tides:

28. Synchronous Rotation The Moon’s near side is always towards the Earth.
Moon has become tidally locked to the Earth.