Q&A for How to Prove the Earth Is Round

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  • Question
    How do we know that the Earth is round?
    Community Answer
    When a ship on the ocean is going further away it does not just get smaller and smaller, but instead the level of the ship (relative compared to you) drops, thus proving the Earth round. If the Earth was flat, then the ship would just decrease in size, not drop.
  • Question
    Is there anything in the sky that is not actually round?
    Han
    Community Answer
    Many meteoroids and comets aren't round. For example, take a look at comet 67P: it consists of two smaller lobes. Small objects like this often have an irregular shape because they don't have enough gravity to contract into a sphere.
  • Question
    What is the approximate shape of Earth?
    Hannah
    Community Answer
    It's not a perfect sphere, but rather an oblate spheroid or ellipsoid, which means that the poles are slightly "squished" together and on the equator, there is a slight bulge. This happens because of the Earth's rotation. The centrifugal force pulls the parts with more mass further away from the rotational axis.
  • Question
    How does rotation differ from orbit?
    Donagan
    Top Answerer
    Rotation refers to an object's spinning about an internal axis. Orbiting refers to an object's movement around an external axis.
  • Question
    How do we know that the Earth is rotating?
    Donagan
    Top Answerer
    Nowadays we can watch it spin from an outpost such as the Moon. Before we were able to do that, we relied on devices such as the Foucault pendulum. See Wikipedia's article on that.
  • Question
    What is meant by the Earth's rotation?
    Donagan
    Top Answerer
    That refers to the Earth's spin around its own axis.
  • Question
    If the shape of the Earth is not a perfect sphere, then what could be the best shape that we can give to the Earth's shape?
    Donagan
    Top Answerer
    The Earth can be described as a "squashed" sphere, with an equatorial diameter slightly greater than its polar diameter.
  • Question
    Why do these questions assume that the sun is enormous?
    Community Answer
    No assumptions are required. Using triangulation and the transits of Venus and Mercury across the face of the Sun, we can accurately determine the distance between the Sun and Earth. Then, using the angular displacement of the Sun from our vantage point, it's easy to determine the Sun's diameter.
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