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# MOON'S DIAMETER WITH A PHOTO

## What do you need?

• A pen and a piece of paper.
• Some knowledge related with telescopes
• How to obtein the formula If some dynamic worksheets are not available, java can be download from: http://www.houspain.com/gttp/salsaj

## Exercise

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, • the distance from the Earth to the Moon is 384,444 km
• Two formulas: and  ##### 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.
• 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.

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