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Shape of the Earth

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Shape of the Earth How a scientific proof works. What is Earth s shape? Is it flat like a coin, or spherical like a ball? Perhaps it s like a tin can, flat on the ... – PowerPoint PPT presentation

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Date added: 23 January 2020
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Title: Shape of the Earth


1
Shape of the Earth
  • How a scientific proof works.

2
What is Earths shape?
  • Is it flat like a coin, or spherical like a ball?
    Perhaps its like a tin can, flat on the ends and
    round in the middle?
  • Describe the evidence that best supports you
    answer.

3
Spherical Earth?
  • Scientists claim that Earth is much like a
    slightly flattened ball - an oblate spheroid.
  • How do they know or do the merely have faith in
    the claim?
  • What is the evidence that supports a scientific
    belief in a roughly spherical Earth?

4
Ships appear to sink gradually below horizon from
bottom up.
5
Polaris, the North Star
Polaris
  • is located practically over the North Pole
    of planet Earth.

  • If you stood at the
    North Pole, Polaris
    would be almost
    directly overhead.

6
Why do observations of Polaris help determine
Earths shape?
  • The North Star gradually appears lower and lower
    in the sky as you travel toward the equator.
  • When the North Star is visible at the horizon,
    you are located at the equator.
  • South of the equator the North Star is not
    visible at all.
  • These observations are possible only for a
    roughly spherical Earth.

7
Lunar Eclipses
  • Only a sphere can cast a shadow that always
    appears round. During lunar eclipses, Earth
    casts its shadow on the moon and the shadow is
    always round.

8
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9
Many other indications
  • Circumnavigation of the globe.
  • Existence of time zones.
  • Earth-orbiting satellites.
  • Photographs from space.
  • Eyewitness reports of astronauts.
  • Other objects - sun, moon, planets - are roughly
    spherical.

10
Summary How do we know the Earth to be
spherical?
  • Ships appear to sink GRADUALLY below the horizon
    as they travel away from observer and over the
    horizon - in all directions.
  • Polaris (North Star) changes altitude (angle
    measured in degrees above earths surface) with
    latitude at all longitudes.
  • Lunar Eclipses - Earths shadow on the moon is
    always round.
  • Satellite imagery and much more.

11
Is Earth perfectly spherical?
  • The Earth is NOT a perfect sphere
  • It is flattened at the poles and bulges at the
    equator due to its spinning.
  • Earth is very slightly out of round or OBLATE.
  • Saturn is an even better example
    of being oblate.

12
What proof is there that the Earth is slightly
oblate?
  • Gravity measurements. Gravity is the force of
    attraction between any two objects.
    Increase mass of objects increase gravity
    Decrease distances increase gravity
  • If Earth were a perfect sphere, it would be
    expected to exert an equal force on objects at
    equal distances from the center of earth.

13
The pull of gravity is weaker farther from the
center of Earth
You weigh just a bit less at the equator than at
the pole!
14
The Oblate Sphere
  • The difference with a sphere is small
  • We can not see it with the naked eye
  • Earth still appears like a sphere

15
Why is Earth not perfectly round?
  • Earths spinning (rotation) causes
  • bulging at equator and
  • flattening at the poles.
  • Be careful on multiple-choice tests!

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