# The Shape of the Earth - PowerPoint PPT Presentation

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## The Shape of the Earth

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### Lunar eclipses show the curved shadow of the earth on the moon. ... On a spherical earth, if you are on the equator, Polaris is on the horizon. ... – PowerPoint PPT presentation

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Title: The Shape of the Earth

1
The Shape of the Earth
2
Once thought to be flat
3
Observations you can make support a round earth.
Lunar eclipses show the curved shadow of the
earth on the moon.
4
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5
Observe a ship leaving the shore.
6
As it gets further away it gets smaller but.
7
On a flat earth, as the ship sails away it
appears small but you see all parts.
8
On a round earth ..
9
the ship drops over the horizon.
10
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11
The ship gets smaller but disappears from the
bottom up.
12
Lastly the pole star , Polaris is proof the earth
is a sphere.
13
If you can find the Big Dipper you can find
Polaris.
14
The altitude of Polaris changes with your
position on the earth.
15
Try the following activity to see why
16
On a spherical earth, if you are on the equator,
Polaris is on the horizon.
17
In Pleasantville, Polaris is about half way
between the horizon and the zenith.
18
At the North Pole, Polaris is directly overhead.
Polaris is at the zenith.
19
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.

20
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 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.

21
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
22
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?