1. The Cycles of the Moon

2. Moon Basics…? What is the period of the Moon?
What are the phases of the Moon?
When can you see the different phases of the Moon?
Does the Moon rotate as is revolves?
Does the Moon cause our tides?
What are tides?
What are eclipses?
Can we predict them?

3. Sidereal Period (1)
The Sidereal period is the time it takes the moon to go around Earth WITH RESPECT TO THE STARS.
Start with the moon lined up with some background stars. Now have the moon revolve around Earth.

4. Sidereal Period (2)
From our position on Earth, the moon goes around and then is again lined up with the stars behind it.
Sidereal Period
27.32 days

5. Sidereal Period (3)
Note, however, that the moon no longer lines up with the Sun. It would need to go a bit further for that.
Sidereal Period
27.32 days

6. Synodic Period
The Synodic period is the time it takes the moon to go around Earth WITH RESPECT TO THE SUN.
Synodic
29.53 days
The moon must go a bit further to line up with the Sun again.
Sidereal
27.32 days

7. Sunlight

8. Sunlight

9. Sunlight

10. 1st Quarter
Waxing
Crescent
Waxing
Gibbous
Full Moon
New Moon
Waning
Waning
Gibbous
Crescent
3rd Quarter

11. Which phase is overhead at…? What time is the phase overhead…?
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
6 pm
9 pm
3 pm
Midnight
Noon
3 am
9 am
6 am
Which phase is overhead at…?
What time is the phase overhead…?

12. Rise Set Phase 1st Quarter Full Moon 3rd Quarter New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
Noon
Midnight
3 pm
6 pm
9 pm
9 am
6 am
3 am
Rise
Set
Phase
What time does the 1st Quarter moon rise? Set?
Point the arrow at the phase and it will tell you the rise and set time.
The 1st Quarter rises at noon and sets at midnight.

13. Rise Set Phase 1st Quarter Full Moon 3rd Quarter New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
Noon
Midnight
3 pm
6 pm
9 pm
9 am
6 am
3 am
Rise
Set
Phase
What time does the Waxing Gibbous moon rise? Set?
Point the arrow at the phase and it will tell you the rise and set time.
The Waxing Gibbous rises at 3 pm and sets at 3 am.

14. Set Rise Phase What time does the Waning Crescent moon rise? Set?
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
Noon
Midnight
3 pm
6 pm
9 pm
9 am
6 am
3 am
The Waning Crescent rises at 3 am and sets at 3 pm.
Rise
Set
Phase
Point the arrow at the phase and it will tell you the rise and set time.

15. 1st Quarter Full Moon 3rd Quarter New Moon Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
Noon
Midnight
3 pm
6 pm
9 pm
9 am
6 am
3 am
Which phase rises at…?
Which phase sets at…?

16. Which phase is overhead at 11 pm? The “phase” rises at…?
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
Noon
Midnight
3 pm
6 pm
9 pm
9 am
6 am
3 am
Which phase is overhead at 11 pm?
The “phase” rises at…?
The “phase” sets at…?

17. There are 4 points to the orbit 1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
and 4 areas.
6 pm
9 pm
3 pm
Midnight
Noon
3 am
9 am
6 am
Which phase is overhead at 11 pm?
Waxing Gibbous

18. Which phase rises/sets at…?
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
Noon
Midnight
3 pm
6 pm
9 pm
9 am
6 am
3 am
Which phase rises/sets at…?

19. East Rise Set West Phase Using the paper method
If you went out at 6 pm on the night of the full moon, which way would you look to see it?
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
Noon
Midnight
3 pm
6 pm
9 pm
9 am
6 am
3 am
East
6 pm is on the East side.
Rise
Set
Phase E W
West
You would look to the East.
The Full Moon would be rising on your eastern horizon.
Which way would you look to see…?

20. Set West Rise East Phase Using the paper method
If you went out at 6 pm on the night of the waxing crescent, which way would you look to see it?
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
Noon
Midnight
3 pm
6 pm
9 pm
9 am
6 am
3 am
6 pm is on the West side.
Rise
Set
Phase
East
West
You would look to the West.
The waxing crescent would be setting in the west.
Which way would you look to see…?

21. Counterclockwise = East Clockwise = West
In your head method
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
Noon
Midnight
3 pm
6 pm
9 pm
9 am
6 am
3 am
Counterclockwise = East
Clockwise = West
Start at the time
Rotate toward the phase
If you went out at 6 pm on the night of the full moon, which way would you look to see it?
You would look in a counterclockwise direction… East.
The Full Moon would be rising on your eastern horizon.
Which way would you look to see…?

22. Counterclockwise = East Clockwise = West
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
Noon
Midnight
3 pm
6 pm
9 pm
9 am
6 am
3 am
Counterclockwise = East
Clockwise = West
If you went out at 6 am on the night of the waning gibbous, which way would you look to see it?
Start at the time
Rotate toward the phase
You would look in a clockwise direction… West.
Which way would you look to see…?

23. Counterclockwise = East
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
Noon
Midnight
3 pm
6 pm
9 pm
9 am
6 am
3 am W E
Clockwise = West
Counterclockwise = East
Which way would you look to see…?

24. Counterclockwise = East Clockwise = West
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
Noon
Midnight
3 pm
6 pm
9 pm
9 am
6 am
3 am
Counterclockwise = East
Clockwise = West E W
New Moon (but you can’t see it), waxing crescent, 1st Quarter, Waxing Gibbous, Full Moon.
There are always 5 possibilities!
If you went out at 6 pm every night for a month, which phases would you see?

25. Counterclockwise = East Clockwise = West
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
Noon
Midnight
3 pm
6 pm
9 pm
9 am
6 am
3 am
Counterclockwise = East
Clockwise = West E W
Waxing Gibbous, Full Moon, Waning Gibbous, 3rd Quarter, Waning Crescent
There are always 5 possibilities!
If you went out at 1 am every night for a month, which phases would you see?

26. Counterclockwise = East
1st Quarter
Full Moon
3rd Quarter
New Moon
Waxing Crescent
Waxing Gibbous
Waning Gibbous
Waning Crescent
Noon
Midnight
3 pm
6 pm
9 pm
9 am
6 am
3 am W E
Clockwise = West
Counterclockwise = East
What phases would you see during the month at…?

27. Other websites
A good tool to test yourself on moon phases can be found at:
This tool requires JAVA.
This website also has a good moon tutorial.
This is a great animation of moon phases!

28. The Tides
Tides are due to gravitational force on Earth from Moon – force on near side of Earth is greater than force on far side. Water can flow freely in response.

29. Spring and Neap Tides
The Sun is also producing tidal effects, about half as strong as the Moon.
Near Full and New Moon, those two effects add up to cause spring tides.
Near first and third quarter, the two effects work at a right angle, causing neap tides.
Spring tides
Neap tides

30. The Tides
Tides tend to exert a “drag” force on the Earth, slowing its rotation.
This will continue until the Earth rotates synchronously with the Moon, so that the same side of the Earth always points toward the Moon.

31. Acceleration of the Moon’s Orbital Motion
Earth’s tidal bulges are slightly tilted in the direction of Earth’s rotation.
Gravitational force pulls the moon slightly forward along its orbit. This causes the Moon to recede at 2” per year. (3.8 cm)

32. The Tidally-Locked Orbit of the Moon
The Earth also exerts tidal forces on the moon’s rocky interior.
 It is rotating with the same period around its axis as it is orbiting Earth (tidally locked).
 We always see the same side of the moon facing Earth.

33. The Tidal Effects
Io – resonant orbital interactions between Io and Europa, Ganymede, and Jupiter cause 100 m tidal bulges that move, stretch and bend the moon.
Pluto and Charon – tidally locked.
Bay of Fundy – The difference between high and low tide can be 48 feet – 5 stories tall!

34. Eclipses
Eclipses occur when Earth, Moon, and Sun form a straight line

35. Motion of the Moon
Eclipses don’t occur every month because Earth’s and Moon’s orbits are not in the same plane.

36. Conditions for Eclipses (1)
The moon’s orbit is inclined against the ecliptic by ~ 50.
A solar eclipse can only occur if the moon passes a node near new moon.
A lunar eclipse can only occur if the moon passes a node near full moon.

37. Lunar Eclipses
Earth’s shadow consists of a zone of partial shadow, the Penumbra, and a zone of full shadow, the Umbra.
If the moon passes through Earth’s full shadow (Umbra), we see a lunar eclipse.
If the entire surface of the moon enters the Umbra, the lunar eclipse is total.

38. A Total Lunar Eclipse

40. Aug 2007 Eclipse

41. A Total Lunar Eclipse
A total lunar eclipse can last up to 1 hour and 40 min.
During a total eclipse, the moon has a faint, red glow, reflecting sun light scattered in Earth’s atmosphere.

42. Typically, 1 or 2 lunar eclipses per year.

43. Solar Eclipses
The sun appears approx. as large in the sky (same angular diameter ~ 0.50) as the moon.
 When the moon passes in front of the sun, the moon can cover the sun completely, causing a total solar eclipse.

44. Solar Eclipse – China 2009

45. Diamond Ring Effect

46. Solar Atmosphere Revealed

47. Moon Shadow on Earth

48. Solar Eclipses:
Approximately 1 total solar eclipse per year

49. Earth and Moon’s Orbits Are Slightly Elliptical
Apogee = position furthest away from Earth
Earth
Perihelion = position closest to the sun
Moon
Perigee = position closest to Earth
Sun
Aphelion = position furthest away from the sun
(Eccentricities greatly exaggerated!)

50. Annular Solar Eclipses
The angular sizes of the moon and the sun vary, depending on their distance from Earth.
When Earth is near perihelion, and the moon is near apogee, we see an annular solar eclipse.
Perigee
Apogee
Perihelion
Aphelion

51. Annular Solar Eclipses (2)
Almost total, annular eclipse of May 30, 1984

52. The Saros Cycle
The cycle is days.
~ 18 years 11 1/3 days.