Moon Phases,
and Eclipses
• Motions of the Moon
– Moon revolves around
the Earth and rotates
on its axis.
• Takes 27.3 days to
revolve around Earth.
• Rotates slowly on its
axis, once every 27.3
days.
– Earth only sees the
same side of the moon.
• “Far side” always faces
away.
• Phases of the Moon
– We see the moon
because it reflects light
from the sun.
– The moon’s shape
changes during the
month causing the
phases.
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• Phases of the Moon
– New Moon
• The sun lights the side
of the moon facing
away from Earth. This
side of the moon that
faces the Earth is
dark.
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• Phases of the Moon
– Waxing Crescent
• You see more and
more of the lighted
side of the moon.
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• Phases of the Moon
– First Quarter
• You see half of the
lighted side of the
moon.
• The moon is ¼ of the
way through it’s orbit.
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• Phases of the Moon
– Waxing Gibbous
• The moon continues
to wax.
• The moon is called a
waxing gibbous.
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• Phases of the Moon
– Full Moon
• The whole lit side of
the moon can be seen
from Earth.
• This is known as a Full
Moon.
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• Phases of the Moon
– Waning Gibbous
• The Moon now
becomes darker each
day. This is known as
a waning gibbous
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• Phases of the Moon
– Third Quarter Moon
• You can see half of
the moon’s lit side.
The moon is ¾ of the
way through it’s orbit.
This is called a third
quarter moon, or last
quarter moon.
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• Phases of the Moon
– Waning Crescent
• The last phase before
new moon.
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F
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• Phases of the Moon
– Phases are caused by
changes in the relative
positions of the moon,
Earth and sun.
• As the moon revolves
around the Earth, we see
the moon from different
angles.
– The phase of the moon
depends on how much of
the sunlit side of the
moon faces Earth.
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• Phases of the Moon
– The cycle begins at
new moon.
– The amount of light on
the moon will
gradually increase
(Waxing) to full moon.
– After full moon, the
light will gradually
decrease (Waning)
back to new moon.
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Objective: I will be able to describe how the
Moon moves and what causes the phases.
• Phases of
the Moon
– One lunar
cycle lasts
29.5 days.
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• Eclipses
– The moon’s orbit is
slightly tilted.
– As a result, the
moon doesn’t always
pass into the Earth’s
shadow or the
shadow from the
moon isn’t cast on
the Earth.
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• Eclipses
– When the moon’s shadow
hits the Earth or the Earth’s
shadow hits the moon, an
eclipse occurs.
– An eclipse occurs when an
object in space comes
between the sun and a third
object and casts a shadow
on that object.
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• Solar Eclipse
– Occurs when the moon is in the new moon
phase and it passes between the Earth and
the sun.
– Blocking sunlight from the Earth.
– The moon’s shadow hits the Earth.
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• Total Solar Eclipse
– Occurs when the
darkest part of the
moon’s shadow, “the
umbra” hits the Earth.
• Sunlight is completely
blocked in any part of
this shadow.
• Must be in the shadow
of the umbra to see a
total solar eclipse.
• Stars, and the corona
are visible.
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• Partial Solar Eclipse
– Occurs when the less
dark shadow “the
penumbra” hits Earth.
– People in the penumbra
only see a partial
eclipse.
– Part of the sun is still
visible.
• It is not safe to look
directly at the sun.
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• Lunar Eclipse
– Occurs at a full moon when the Earth is
directly between the moon and the sun.
– Earth blocks sunlight from reaching the moon.
– The moon is in the shadow and looks dark.
– Can only occur during a full moon.
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• Total Lunar Eclipse
– Occurs when the moon
is in the Earth’s “umbra”
• The dark shadow.
– Can be seen anywhere
on the dark side of the
Earth where the moon
is visible.
– More likely to see a
lunar eclipse than a
solar eclipse.
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• Partial Lunar Eclipse
– Occurs if the Earth,
moon and sun are not
quite in a line.
– The moon only partially
passes into the umbra
of the Earth’s shadow.
• Edge of shadow appears
blurry.
• Last up to 2 or 3 hours.
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