Thanks for the ideas. I played around with a few ideas of my own and found the way that worked for me. The finished image is here:
http://www.astonshell.com/forum/viewtopic.php?t=5173&start=15 (near the bottom) Here is how I did it in Photo Shop:
1) make a selection of the innermost circle.
2) select/modify/contract 2px
3) using the square selection and alt (on a PC of course

) deselect the upper half of the selection.
4) then using the circle selection tool with a set height and with of 36px x 46px and alt, deselect the middle part of the selection leaving a semi circle that had a thinner base that gets wider as it goes. (I don't know if I explained that well.)
5) fill in the selection.
6) create a new layer and freehand marks that show where you are going to erase.
7) get the eraser tool and select the layer with the filled selection on it.

erase where ever your marks are.
This worked quite nicely for me.