The impact theory proposes that the Moon formed from the debris ejected into Earth's orbit after a Mars-sized body collided with Earth. The Moon rotates in sync with its revolution around Earth, always showing the same face. Its daily eastward movement against the stars is due to revolution, while its rising and setting is caused by Earth's rotation. The changing visible shape of the Moon, from new to full and back, is due to its position in its orbit around Earth. Lunar and solar eclipses occur when the Moon blocks the Sun or enters Earth's shadow, respectively, but not every month due to the Moon's tilted orbit. Tides are caused by the gravitational pull of the Moon and Sun, with spring

1. IMPACT THEORY OF MOON
FORMATION

4. Moon Orbits the Earth – but appears to
rise in the east and set in the west due
to earth’s faster rotation

6. Moon’s Rotation = Moon Revolution
 rotation period =
27.3 days
 revolution period =
27.3 days
 Moon shows the same
“face” to the Earth
 Velocity: 360°/27.3
days = 13° per day

8. Daily Movement of the Moon
• Each day the Moon rises in the east and sets
in the west as a result of the Earth's rotation.
• It moves about 13° eastwards against the
background of stars as a consequence of its
revolution around the Earth.

10. Moon Phases
 Half of the moon is always receiving light
from the sun.
 The “lit” portion that is visible to earth
varies as the moon REVOLVES around
earth. THIS CAUSES THE PHASES OF
THE MOON.
 Visible portion of moon growing = waxing
 Visible portion of moon shrinking = waning

11. Lunar Phases

15. How much of the moon we see depends on where the
moon is in its orbit:
Appearance:

16. Appearance:

17. Appearance:

18. What we observe from
earth

22. Cycle of Lunar Phases
 Takes 29.53 days
 This is because when moon gets back to its
original position in 27.3 days, the earth has
moved 1°/day or about 27°.
 The moon moving at l3°/day takes about 2
days to catch up with Earth and align with it
and the sun in a new moon phase.

24. Lunar and Solar Eclipses
The Moon orbits the Earth, and travels
with the Earth about the Sun.
Sometimes the Moon gets between the
Earth and the Sun, causing solar
eclipses, and sometimes the Moon
goes into the Earth's shadow, causing
lunar eclipses.

25. Solar Eclipses – can occur only
during the new moon phase
Lunar eclipses – can occur only
during the full moon phase

26. The Cause of Eclipses:
Shadows

30. Lunar Eclipses

31. Solar Eclipses

33. If Lunar eclipses happen in the full moon phase and
solar eclipses happen in the new moon phase, why
don’t they happen every month???
As the Moon orbits the Earth, its orbit is tilted slightly
(about 5 degrees) from earth’s orbital plane (ecliptic)
The moon crosses earth’s plane twice during its orbit. If
this crossing happens at the new moon phase, the Moon
will be lined up with the Sun and pass in front of it.
This alignment has to be perfect in order for the Moon to
completely cover the Sun for a total solar eclipse (the
sky will darken just like nighttime, and the stars will be
visible) Total solar eclipses last about 7 minutes and
occur in a very narrow range across Earth. Full moon
phase = total lunar eclipse if perfect.

34. Solar Eclipses Occur when moon’s
orbit intersects ecliptic during the
new moon phase

36. Total Solar Eclipses only last about 7
minutes in a very narrow range across
Earth

37. Daily Cycle of Tides
 Driven by the gravitational pull of the moon and Sun
 Affected by nearness of the moon more than the size of
the Sun
 As earth rotates, the tides move around the Earth
alternating between high and low tides approximately
every 6 hours.

41. Spring Tides – Neap Tides
 Tidal range: Difference
in height between high tide
and low tide
 Spring Tides: new and
full moon phase – greatest
range
 Neap Tides: 1st and 3rd
Quarter phases – smallest
range

43. Moon motion like all celestial bodies except
planets which sometime appear to undergo
Retrograde Motion

44. Retrograde Motion