Phases of the Moon, Eclipses and Tides

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Phases of the Moon, Eclipses and Tides

1. What are the rotation and revolution periods of
   the Moon? (p.646)
2. What causes the Moon to shine? (p.647)
3. What are the phases of the Moon? (pp.647-48)
4. What causes solar eclipses? Where and how often
   do they occur? (p.649)
5. What causes lunar eclipses? (pp.650)
6. What causes the ocean tides on Earth? (p.533)

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Phases of the Moon

• Just as the earth rotates and revolves around the
  sun, the moon rotates and revolves around the
  earth.
• It takes the moon 27.3 days to rotate on its axis
  and 27.3 days to revolve around the earth.
• We can only see the part of the moon that the sun
  is shining on. This, along with the rotation of
  the moon results in the phases of the moon

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• New moon The dark side of the moon completely
  faces us, and the moon appears invisible.
• Waxing phases The bright side of the moon moves
  into view, the moon appears to be getting larger.
• Quarters Half the dark side and half the bright
  side face us. The moon looks like it has been
  cut in half.
• Full moon The bright side is completely facing
  us and the moon is completely visible.
• Waning phases The bright side of the moon moves
  out of view, the moon appears to be getting
  smaller.

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2. What causes the Moon to shine?

• The moon does not actually give off any light of
  its own. It reflects the light of the Sun which
  shines on it back to Earth.
• When the lighted side of the moon is facing us,
  the moon appears fully lit (called a Full Moon).
• When the lighted side of the moon is facing away
  from Earth, the moon appears dark. (called a New
  Moon).

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New Moon
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Waxing Crescent
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Waxing Crescent
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First Quarter
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Waxing Gibbous
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Waxing Gibbous
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Full Moon
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Waning Gibbous
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Waning Gibbous
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Last Quarter
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Waning Crescent
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Waning Crescent
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New Moon
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What causes solar eclipses? Where and how often
do they occur?

• A Solar Eclipse occurs when the Moon moves
  directly between the Earth and the Sun, and casts
  its shadow over part of the Earth.
• Solar eclipses can either be total (the entire
  sun is blocked), partial (only part of the Sun
  blocked) or annular (the middle is blocked,
  leaving a ring of light).

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Solar Eclipses (cont.)

• As seen from this location, the entire event
  takes about 2 hours. The Sun is only completely
  eclipsed for about 1 minute, and then slowly
  uncovered over an hour. This is a time lapse
  multiple exposure photo showing the entire 2002
  solar eclipse in Africa.

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Solar Eclipses (cont.)

• Only a narrow band of Earth experiences a total
  eclipse at any one event (in the Umbra), but a
  large area on either side of the total eclipse
  band sees a partial solar eclipse (in the
  Penumbra), where only part of the Sun is
  blocked.

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Solar Eclipses (cont.)

• Umbra darkest shadow, where the total eclipse
  occurs
• Penumbra lighter shadow, where only a partial
  eclipse occurs

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Solar Eclipses (cont.)

• Eclipses follow an 18 year, 11.3 day cycle called
  the Saros Cycle. This map shows the current
  cycle.

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What causes lunar eclipses?

• When the Earths shadow falls on the Moon, a
  lunar eclipse occurs. Lunar eclipses can be total
  or partial.
• Sunlight reflected through the earths atmosphere
  makes the Moon appear red during a lunar eclipse.

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Lunar Eclipses (cont.)

• The much larger umbra cast by Earth allows the
  entire night hemisphere of Earth to see a total
  lunar eclipse, provided the sky is clear.

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The moon is usually at a slight angle above or
below the equator (5.2), and is not in the
Earths shadow. At times, the moon is not at the
angle and an eclipse can be seen instead of a
full moon. This can happen 2-3 times a year
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What causes the ocean tides on Earth?

• Tides are caused by gravitational attraction
  between the Earth, Moon, and Sun. The Moon
  exerts a stronger pull on Earth than does the Sun
  because it is closer
• Water in the oceans bulges toward the Moon, and
  thus causes a high tide on the sides of Earth
  facing towards and away from the Moon.
• When the Moon and Sun are on opposite sides of
  Earth from one another, the tides are highest.
  These are called Spring Tides.
• Neap Tides occur when the Sun and Moon are at
  right angles to one another. They are lower.

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• The position of the moon affects the intensity of
  the tides.
• When the moon is aligned with the sun and Earth,
  Spring tides occur.
• When the moon is at a angle to the sun and Earth,
  Neap tides occur.

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