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The photo below has been taken with a telescope (that has focal distance = 18.56m).
Knowing distance from Earth to the Moon is 384444 km, find out Moon's diameter.

Working out

What do we know?
  • Focal length of the telescope, f = 18.56 m
  • the distance from the Earth to the Moon is 384,444 km
  • Two formulas: s = 0.0174f and D = rθ

What do we have to find out?
  • We'd like to work out the Moon's diameter, D, this being twice the radius, R.
Work out
  • With the programm SalsaJ, open the photos below and measure diameter's moon (mm). We'll call this value “u”. The scale of each photo is below them.


Escala:                                 0.06 píxel/Km.                                1.15 píxel/Km.

  • The focal lenght of the telescope is f = 18.56 m, so we can claculate s using the formula s = 0.0174f.
  • Find out the angular diameter with θ=u/s, since we know u and s.
  • Transform this value into radians (just multiply it by 0.0174
  • Since we know that the distance from Earth to Moon is roughly 384,444 km, we can find out Moon's diameter, D, from θ y r (the distance from we to the object.

telescope_focal.txt · Última modificación: 24/04/2017 13:13 (editor externo)
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