Radius of the Earth

This proof uses the fact that the earth is a sphere, trigonometry, and the geometry of a circle.

  1. Due to the fact that the sun is so far away, the sunlight that hits the earth are parellel to each other.
  2. Pick two locations that are away from each other.
  3. Put a meter stick into the ground.
  4. At exactly the same time, measure the length of the stick's shadow that is cast by the sun
  5. Using trigonometry, we can compute the angle that the sun's light makes with the stick
  6. Compute the difference between the two angles
  7. Solve for X in (Angle Difference) / 360 = (Distance between points) / X
  8. X is the circumference of the earth. The radius of the earth is R = X / (2 * pi)

Return home