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Step 3Marking Out
The base plate of the dial is where everything happens, so it makes sense to take your time getting it ready.
I scored little grooves into mine to absorb and protect the permanent marker (i don't know what from). You don't need to do this. Also, I have far too many lines on mine which makes it difficult to see the shadow.
First, you'll need to find the centre. I used a ruler but there are many ways of doing it.
From the centre, draw the little circle in the middle a third the size of the plate (a ruler and a pocket calculator is probably the simplest means of finding the right size).
In the little circle, draw a line from one side to the other, straight through the middle. You'll end up aligning the shadow with this line, so don't clutter it like I did.
You also need to put little marks at the edges of the plate in line with this line, these marks will become markers for the solstices (20th of dec and 20th of june).
In the end, you'll need marks for the equinoxes to line the dome up with; these are simply at right angles to the solstice marks.
On a piece of paper, draw a circle the same size as the base plate, this will help you to set your compass to the right distances to mark the plate neatly.
Going back to high school geometry, or Wikipedia, divide this circle into six arcs by tracing a circle the same size from one point on the edge to another point on the edge, all the way around the circle.
Then bisect one of these arcs, giving you marks for a twelfth of a circle.
*Remember, this is on paper, so you only need to get one of any length to set the compass.
You also need to find an arc that's a third the length of one of these 12 arcs (I had to resort to trial-and-error at this point)
I scored little grooves into mine to absorb and protect the permanent marker (i don't know what from). You don't need to do this. Also, I have far too many lines on mine which makes it difficult to see the shadow.
First, you'll need to find the centre. I used a ruler but there are many ways of doing it.
From the centre, draw the little circle in the middle a third the size of the plate (a ruler and a pocket calculator is probably the simplest means of finding the right size).
In the little circle, draw a line from one side to the other, straight through the middle. You'll end up aligning the shadow with this line, so don't clutter it like I did.
You also need to put little marks at the edges of the plate in line with this line, these marks will become markers for the solstices (20th of dec and 20th of june).
In the end, you'll need marks for the equinoxes to line the dome up with; these are simply at right angles to the solstice marks.
On a piece of paper, draw a circle the same size as the base plate, this will help you to set your compass to the right distances to mark the plate neatly.
Going back to high school geometry, or Wikipedia, divide this circle into six arcs by tracing a circle the same size from one point on the edge to another point on the edge, all the way around the circle.
Then bisect one of these arcs, giving you marks for a twelfth of a circle.
*Remember, this is on paper, so you only need to get one of any length to set the compass.
You also need to find an arc that's a third the length of one of these 12 arcs (I had to resort to trial-and-error at this point)
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Jan 4, 2010. 6:49 PMusb key
says:
according to WIKIPEDIA! WOOT WOOT!!!1 the summer solstic is either the 20th or the 21st and the winter solstic is the 21st or 22nd depending on wether or not its a leap year. doesnt really make a difference, just felt like correcting you
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