I have a sort of template thing, not ruler. it has sort of curving lines that are slits through plastic to mark through. it's somewhere. I think I used it once. you can mark with a straight ruler. just watch how far apart on each side of the center line you mark. When I think sun burst I think radiating lines going outward, like rays of sunshine. mark with caulk or a plastic hera marker if it would show on your fabric well.