Phases, Eclipses, and Tides

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Phases, Eclipses, and Tides
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Phases, Eclipses, and Tides

• As the moon revolves around Earth and Earth
  revolves around the sun, the relative positions
  of all of them change.
• These positions cause the phases of the moon,
  eclipses, and tides.

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Motions of the Moon

• The moon's orbit around Earth is an oval shape.
• The moon rotates slowly on its own axis once
  every 27.3 days.
• Because it revolves around Earth every 27.3 days,
  a day and a year on the moon are the same
  length.
• The same side of the moon, the near side,
  always faces Earth.
• The far side of the moon always faces away from
  Earth, so you never see it from Earth.

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Motions of the Moon
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Phases of the Moon

• The moon does not produce the light you see. It
  reflects light from the sun.
• The different shapes of the moon you see from
  Earth are called phases.
• The moon goes through all the phases each time it
  revolves around Earth and each shape may change
  every 3-4 days.
• about once a month.

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Phases of the Moon
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What Causes Phases?

• Phases are caused by changes in the relative
  positions of the moon, Earth, and the sun.
• The sun lights the moon.
• The phase of the moon you see depends on how much
  of the sunlit side of the moon faces Earth.

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The Cycle of the Phases

• During the new moon, the side of the moon facing
  Earth is not lit.
• As the moon revolves around Earth, you see more
  and more of the lighted side of the moon every
  day, until the side of the moon you see is fully
  lit.
• About 29.5 days after the last new moon, the
  cycle is complete, and you see a new moon again.

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Eclipses

• In most months the moon revolves completely
  around Earth without the moon moving into Earth's
  shadow or the moon's shadow hitting Earth.
• When the moon's shadow hits Earth or 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.
• There are two types of eclipses solar eclipses
  and lunar eclipses.

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The Tilt of the Moon's Orbit

• The moon's orbit is tilted with respect to
  Earth's orbit.
• So the moon rarely goes directly between Earth
  and the sun

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Solar Eclipses

• A solar eclipse occurs when the moon passes
  between Earth and the sun, blocking the sunlight
  from reaching Earth.
• The moon's shadow then hits Earth.

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Solar Eclipses
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Total Solar Eclipses

• The darkest part of the moon's shadow, the umbra,
  is cone-shaped.
• From any point in the umbra, light from the sun
  is completely blocked by the moon.
• The moon's umbra happens to be long enough so
  that the point of the cone can just reach a small
  part of Earth's surface.

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Lunar Eclipses

• A lunar eclipse occurs at a full moon when Earth
  is directly between the moon and the sun.
• During a lunar eclipse, Earth blocks sunlight
  from reaching the moon.
• The moon is then in Earth's shadow and looks dark
  from Earth.
• Because the moon is closest to Earth's shadow
  during the full moon, lunar eclipses occur only
  at full moon.

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Lunar Eclipses
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Total Lunar Eclipses  

• When the moon is in Earth's umbra, you see a
  total lunar eclipse.
• You can see Earth's shadow on the moon before and
  after the total part of a lunar eclipse.
• Unlike a solar eclipse, a lunar eclipse can be
  seen anywhere on Earth that the moon is visible.

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Tides

• Tides, the rise and fall of water, every 12.5
  hours or so.
• The force of gravity pulls the moon and Earth
  (including the water on Earth's surface) toward
  each other.
• As Earth rotates, the moon's gravity pulls water
  toward the point on Earth's surface closest to
  the moon.