What is this star shaped symbol on the tarmac? This symbol is on the tarmac at Ramona, CA airport.  I've seen it at other small GA airports from Google Earth but I don't know what it is.  Can someone please explain?
That is a Compass Rose, painted on a Compass Calibration Pad. It's used to mark a location on the airport surface that is suitable for calibrating the compass of an aircraft.

Here's one in a slightly different style:


and a more basic one from an FAA diagram:


More information on the requirements for the compass rose / compass pad can be found in AC 150/5300-13, in Appendix 6.