Earth

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Topic 2.1

• Earths Dimensions and Navigation

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(No Transcript)
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What is the shape of the Earth?

• spherical

Is there any proof?
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Evidence for a spherical Earth . .

• As ships sail away, they disappear from bottom to
  top.
• As the sun sets, the last of the light lingers on
  the top of the trees.

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Evidence Continued . . .

• The North Star is also called Polaris.
• Polaris is located above the Earths North Pole.

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So what happens to the altitude of Polaris as you
travel north?
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Evidence continued . . .

• The North Star s altitude or height above the
  horizon changes in a predictable way as latitude
  changes.
• As latitude increases, the altitude of Polaris
  increases.

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At the equator, Polaris makes a 0 angle with the
horizon.
horizon
Latitude of Equator 0
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In Auburn, the altitude of Polaris is 43.
horizon
Latitude of Auburn 43
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At the Arctic Circle, the altitude of Polaris is
66.5.
horizon
Latitude of Arctic Circle 66.5
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At the North Pole, the altitude of Polaris is
90. It is directly overhead.
horizon
Latitude of North Pole 90
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More evidence . . .

• During a lunar eclipse, the Earth casts a
  curved shadow.
• Photos taken from space show a spherical Earth.

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Is the Earth a perfect sphere?

• NO!
• Earth is an oblate spheroid - slightly flattened
  at the poles and slightly bulging at the equator.

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Evidence for Shape . . .

• On a true sphere gravity would be the same at all
  latitudes.
• But on Earth, gravity varies with latitude.
• Weight depends on distance from Earths center.

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• Measurements taken by orbiting satellites show
  that the equatorial diameter is larger than the
  polar diameter.