1. The Cycles of the Moon The phases of the moon The tides Lunar eclipses
The Cycles of the Moon
The phases of the moon
The tides
Lunar eclipses
Solar eclipses

2. The Phases of the Moon
From Earth, we see different portions of the Moon’s surface lit by the sun, causing the phases of the Moon.

3. The Moon orbits Earth in a sidereal period of 27.32 days.
The Phases of the Moon
27.32 days
The Moon orbits Earth in a sidereal period of days.
Moon
Earth
Fixed direction in space

4. Is the moon going to show the same lunar phase after one sidereal period?
Yes.
No, it will not have completed a full cycle of phases.
No, it will have completed more than a full cycle of phases.

5. Earth orbits around Sun => Direction toward Sun changes!
The Phases of the Moon
Fixed direction in space
29.53 days
Earth
Moon
Earth orbits around Sun => Direction toward Sun changes!
The moon’s synodic period (to reach the same position relative to the sun) is days (~ 1 month).

6. The moon orbits counterclockwise around Earth (viewed from the North)
The moon orbits counterclockwise around Earth (viewed from the North). => It appears to move eastward against the background of the stars. => The waxing crescent is visible
in the morning sky.
in the evening sky.
the whole night, from sunset to sunrise.
only around midnight.
never.

7. New Moon → First Quarter → Full Moon
The Phases of the Moon
New Moon → First Quarter → Full Moon
Evening Sky

8. Full Moon → Third Quarter → New Moon
The Phases of the Moon
Full Moon → Third Quarter → New Moon
Morning Sky
Waning

9. The Tides
The tides are caused by the difference of the Moon’s gravitational attraction on the water on Earth
Between the near side and the center of the Earth
Between the center and the far side of the Earth
→ 2 tidal maxima
→ 12-hour cycle

10. On the day of full moon, high tides occur …
around noon and 6 p.m.
around noon and midnight.
around 6 a.m. and 6 p.m.
around 6 p.m. and midnight.
Impossible to tell. The times of tides are not correlated with the phases of the moon.

11. 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 w.r.t. each other, causing neap tides.
Spring tides
Neap tides

12. 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.

13. The Near Side of the Moon

14. A total lunar eclipse …
is a high-performance moon vehicle built by Mitsubishi.
occurs when the moon disappears behind the sun.
occurs when the moon becomes invisible because it is too close to the sun.
occurs when the moon moves through Earth’s shadow.
occurs when the moon disappears behind Mars.

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

16. A Total Lunar Eclipse (I)

17. A Total Lunar Eclipse (II)
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 the Earth’s atmosphere.

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

19. The Sun has approx. the same angular diameter of ~ 0.50 as the Moon.
Solar Eclipses
The Sun has approx. the same angular diameter of ~ 0.50 as the Moon.
Thus, when the Moon passes in front of the Sun, it can cover it completely, causing a total solar eclipse.

20. Total Solar Eclipse
Chromosphere and Corona
Prominences

22. Diamond Ring Effect

23. If the sun and the moon have the same angular diameter on the sky, does that mean that the sun and the moon actually have about the same size?
Yes.
No because the sun is much farther away, but also much larger than the moon.
No, because the sun is much farther away, but also much smaller than the moon.
No because the moon is much farther away, but also much larger than the sun.
No, because the moon is much farther away, but also much smaller than the sun.

24. Earth’s 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!)

25. What do you expect to see if at the time of a solar eclipse the moon is near apogee, and the Earth is near perihelion?
A regular total solar eclipse.
No solar eclipse at all.
A partial solar eclipse with a crescent appearance.
A partial solar eclipse with a ring-like appearance of un-occulted parts of the sun.
A lunar eclipse.

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

27. Almost total, annular eclipse of May 30, 1984

28. If the moon was orbiting around the Earth exactly in the plane of the ecliptic, …
lunar and solar eclipses would occur once every day.
lunar and solar eclipses would occur once a week.
lunar and solar eclipses would occur once a month.
lunar and solar eclipses would occur once a year.
lunar and solar eclipses would never occur.

29. Conditions for Eclipses (I)
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.

30. Conditions for Eclipses (II)
Eclipses occur in a cyclic pattern.
→ Saros cycle: 18 years, 11 days, 8 hours

31. Approximately 1 total solar eclipse per year