Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

How to determine the diameter of Earth?

  1. Oct 29, 2011 #1
    We cannot measure the diameter of Earth inch by inch using rulers, and must somehow estimate the distance on Earth, Does anyone have any suggestions on what approach they use to measure the diameter of Earth? and how does this approach apply to measure the diameter of other planets?
    Thanks in advance for any suggestions
  2. jcsd
  3. Oct 30, 2011 #2
    Google Eratosthenes, then google 'The Great Arc' and perhaps 'The Prime Meridian through Paris'.
  4. Oct 30, 2011 #3
    And after that, maybe also google Struve Geodetic Arc
  5. Oct 30, 2011 #4


    User Avatar
    Gold Member

    it doesn't.
  6. Nov 3, 2011 #5
    A planet's diameter may be estimated by occultation, such as studying the cut-off time of a radio signal from an orbiting probe as it swings behind the planet.

    Asteroids have been 'sized' by stellar occultation, where many observers watch for a star's cut-off time. From their position on Earth, the asteroid does or doesn't eclipse a background star.

    Analogy is a solar eclipse, where folk off the centre-line see shorter and shorter eclipses...
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook