Moon Phases

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Moon Phases
Moon Phases Brainstorm
• Think to yourself about the answer to this
question:
What causes the phases of the moon?
Take out a piece of paper and quickly write down
the answer. You have 2 minutes.
Moon Phases
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Full Moon = whole moon illuminated
New Moon = none of the moon is illuminated
Quarter Moon = half moon illuminated
Crescent = less than half of the moon
illuminated
• Gibbous = more than half of the moon
illuminated
Moon Phase Demo
Earth - Moon System
•Moon: a satellite of Earth
•Moon has a radius of
about 0.27 earth radius
•Average distance from
earth = 385,000 km (can
fill with 30 Earth)
The cause of Moon Phases?
• The light that we see from the Moon is
reflected light unlike the Sun, which
emits its own light.
The Earth and the Moon.
Taken by the Galileo spacecraft
(NASA/JPL). The sun provides
the illumination for both the
Earth and the Moon (far right
of the camera’s field of view).
The cause of Moon Phases?
When we take pictures for the tree..
The cause of Moon Phases?
• The light that we see from the Moon is
reflected light unlike the Sun, which emits its
own light.
• The phases of the moon are caused by its
orbital motion.
D
C
B
A
D
C
A
B
We always see only one side of
the moon...
We will always see the same
craters and mountains on
the Moon, no matter when
we look at it.
Caused by Tidal Locking..
• The Moon is tidally locked to the Earth.
• Its rotation period = its orbital period
• Tides caused on the Moon (by the
Earth) created friction that took energy
from the Moon by reducing its spin.
Tidal Force
• We learned the gravitational force
between two objects is
• What if the size of objects is not
negligible..?
Tides
• The tidal force acts on the Earth can
distort the body.
• Earth is rather rigid, so the distortion
effects are small, but the Earth’s oceans
are much more easily deformed.
Tides
• The ocean at point A is closer to the Moon and
experiences a larger gravitational force than
point B and point C.
• Since the Earth rotates (the period is one day),
at given place on Earth experiences high tides
twice per day.
Lecture Tutorial
• Break up into groups of 2-3
– NO MORE THAN 3
• In your group, work through the following:
– The Cause of Moon Phases (pages 79-81)
– Discuss the answers – don’t be silent!
• I will be roaming around if you need help…
• If your group finishes, check your answers
with another group & begin Predicting Moon
Phases (pages 83-85).

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