• Focal length of the telescope,
• the distance from the Earth to the Moon is 384,444 km
• Two formulas: and

• We'd like to work out the Moon's diameter, D, this being twice the radius, R.
  

• 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 , so we can claculate s using the formula .
  
• Find out the angular diameter with , 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 y r (the distance from we to the object.