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# Moon's diameter with image processing

## What do you need?

If some dynamic worksheets are not available, java can be download from: http://www.houspain.com/gttp/salsaj

## Exercise

Calculate the Moon's diameter, helped by "SalsaJ".

## Working out

##### What do we know?
• We know how to get a diameter, drawing a chord.
• We know some properties of the similar rectangle triangles.
• We can use the programm SALSAJ in order to take measurements on a picture given ¡

##### What do we have to find out?
• We are asked to measure the Moon's diameter.

##### Work out
• Open SalsaJ and then open the picture below:

• Draw any line (a chord of the circumference) on the picture.
• This line intersects the edge of the circumference on two points.
• Measure (pixels units) the length of this line between these endpoints.
• Divide it up into equal parts.
• Now you can have the midpoint, M, find it helped by the programm SalsaJ.
• Draw a perpendicular to the line through the midpoint.
• Measure (on that line) the distance from M to the edge of the circunference of the Moon.
• Using your knoledges related with circumference's properties, find out the Moon's diameter.

## To increase

Imagine we had two pictures of the Moon. They are different, they were taken on different dates.
You calculate the Moon's diameter with one of the photos. One of your classmates uses the other one. Your solutionsto the Moon's diameter are different!
What could you deduce from this fact? Do you need a clue?

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