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Earth’s Shape and Size
Unit 1
The Earth’s Shape
• Earth’s shape is
nearly spherical
(Oblate Spheroid)
• It is flattened at
the poles and bulging
at the equator
• This makes a person
weigh slightly more
at the poles than at
the equator
• Earth’s surface is
very smooth
• The height of Mt.
Everest is only
7/10,000 of Earth’s
diameter
Ancient Observations of Earth
• Shadow of Earth during an eclipse
• Position of the stars as travelers moved
north or south
• A ship’s mast disappeared last as it
sailed towards the horizon
• Aristotle, as early as the 3rd century BC
concluded that the earth was a sphere.
Using the North Star
• The North Star (Polaris) appears to
increase in altitude as you travel north
• It is always visible due north to an
observer north of the equator
– 900 for someone at the North Pole
– 00 for someone at the Equator
• If the earth were flat, Polaris would
appear the same to everyone.
Today….
• Photographs from
space are the best
way to see the shape
of the earth
Pre Lab Info
• Roundness Ratio
– Tells us how close something is to a perfect
circle
– A perfect circle would have a roundness
ration of 1 because the diameter would be
the same in all directions
Pre Lab Info
• Scale Models are concrete
representations of an object that is
made in proportion to the object
– They may be larger (ex. Model of an atom)
– They may be smaller (ex. Globe)
Finding the Proportions
• Think ratio: Part to whole = Part to
whole
• Matchbox cars are made on a ratio of
1:59
• This means that the Matchbox car is 59
times smaller than the real car.
• Using the Matchbox car, figure out how
big the real car is.
• 1/59 = 7.1/X
7.1 cm
• X = 418.9 cm
• How many meters is
this?
• 4.189 m