The Shape of the Earth

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The Shape of the Earth
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Once thought to be flat
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Observations you can make support a round earth.
Lunar eclipses show the curved shadow of the
earth on the moon.
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Observe a ship leaving the shore.
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As it gets further away it gets smaller but.
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On a flat earth, as the ship sails away it
appears small but you see all parts.
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On a round earth ..
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the ship drops over the horizon.
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The ship gets smaller but disappears from the
bottom up.
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Lastly the pole star , Polaris is proof the earth
is a sphere.
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If you can find the Big Dipper you can find
Polaris.
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The altitude of Polaris changes with your
position on the earth.
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Try the following activity to see why
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On a spherical earth, if you are on the equator,
Polaris is on the horizon.
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In Pleasantville, Polaris is about half way
between the horizon and the zenith.
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At the North Pole, Polaris is directly overhead.
Polaris is at the zenith.
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To summarize the evidence to support a round
earth

• A lunar eclipse shows the curved shadow of the
  earth.
• A ship dropping over the horizon as it leaves
  the shore.
• The altitude of Polaris is the same as your
  Latitude.

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Today we use instruments that measure gravity to
show the earth is a sphere but not a perfect
sphere.

• Your weight is determined by the pull of gravity
  on your mass.
• On the North Pole you are closer to the center of
  the earth so your weight is slightly higher than
  your weight measured at the equator.

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On the equator you are slightly further from the
center of the earth so you have a lower weight.

• This results from the bulge at the equator.

195N
194N
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But the earth is only slightly oblateIt is
almost perfect. Looking at the earth from space
the earth looks perfectly round. The bulge at
the equator is slight.

• So what is the best model to represent the earth
  a football, an egg, a ping pong ball or an
  orange?