Astrolabe

Why not make a simple astrolabe and plot the changing altitude of the moon over a month? This also works for a star or the sun.

You will need:

 A protractor
 Some string
 Sticky tape
 Blutack or similar to make a weight
 A straw (or biro with the refill and end stop removed)
 Postcard sized card

To Make:
You can download the sheet to help you here.

1) Fix the weight to one end of the string. Fix the other end of the string to the protractor where the zero and 90% lines cross

2) Tape the straw/biro along the flat edge of the protractor so that it over hangs the end by 2cms

3) Make a hole in the middle of the card and push the straw through so that the card makes a mask with the straw as a sight.

To Use:
 
1)  Hold your astrolabe with the straight edge up so the string is free to hang down and swing

2)  Point the straw at the Moon so that you can see it clearly through the straw DO NOT LOOK DIRECTLY AT THE SUN.

3)  When the string stops moving press it against the protractor and read of the number of degrees. This is the altitude of the Moon.

4)  Take regular readings from the same place, for instance every half hour for one night or at the same time every night for a week or more

What changes do you notice?

Plot the points on a graph with time along the horizontal and angle on the vertical. Using a curved line to join plotted points you can predict the height of the Moon for times that have not been observed if cloud has prevented a good sight for instance.

REMEMBER: DO NOT LOOK DIRECTLY AT THE SUN

If you wish to observe the Sun hold a piece of paper in your free hand under your astrolabe. Aim the straw on the astrolabe at the sun and move it closer or further away until a clear image of the sun forms on the paper. You will be able to take measurements from your astrolabe to show the altitude of the sun.

 

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