The Earths shape is an Oblate Spheroid

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The Earths shape is an Oblate Spheroid
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What is an Oblate Spheroid?It is a sphere with
a slight flattening at the polar regions and a
slight bulging at the equatorial
region.Definition The earth is shaped not as a
sphere but as an oblate ellipsoid or geoid (which
simply means "earth shaped.") The earth is widest
at the equator due to gravity and rotation. The
earth is 24,901.55 miles around at the equator
and 24,859.82 miles between the North and South
Poles. The difference between the two is 41.73
miles, so the earth is 41.73 miles wider than it
is tall.
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Eratosthenes

• (276 - 195 B.C.)

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Eratosthenes

• Greek scholar
• called the "father of geography
• educated at the academies of Athens
• Appointed to run the Great Library at Alexandria
  in 240.
• He served as the director of the famous library
  in Alexandria.

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• Having discovered in his reading that a deep
  well at Syene (near the Tropic of Cancer and
  modern Aswan) where sunlight only struck the
  bottom of the well on the summer solstice,
  Eratosthenes determined that he could discover
  the circumference of the earth.
• Eratosthenes measured the altitude of the
  noontime sun at Alexandria at its maximum on Jun
  21st.

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• On that date, the Sun is directly overhead at
  noontime at Syene, in southern Egypt (latitude
  23.5 degrees north).
• The zenith distance is the angle from the zenith
  to the point where the Sun was at noon it is
  also 90 degrees minus the altitude.
• At Syene, the zenith distance was 0 degrees at
  Alexandria it was about 7 degrees.
• He knew how far it was from Alexandria to Syene,
  so he used geometry and the difference in zenith
  angle to estimate the size of the Earth.
• Eratosthenes also measured the tilt of the Earth
  axis by 23.5 degrees, which gives us the seasons
  .

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• In the 17th century, Isaac Newton deduced from
  theoretical considerations that the Earth was
  slightly flattened at the poles and bulged
  slightly at the Equator, due to the Earth's
  rotation on its axis.
• This was subsequently confirmed by field
  observations.
• The Earths equatorial radius is approximately 22
  km longer than its polar radius.
• One consequence of this is that the length of one
  degree of latitude varies slightly depending on
  the distance from the Equator or the poles.

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• The circumference of the earth at the equator is
  24,901.55 miles (40,075.16 kilometers).
• But, if you measure the earth through the poles
  the circumference is a bit shorter - 24,859.82
  miles (40,008 km).
• This the earth is a tad wider than it is tall,
  giving it a slight bulge at the equator.
• This shape is known as an ellipsoid or more
  properly, geoid (earth-like).
• From Matt Rosenberg