Odd Star Test When Cooling Mirror

When my mirror is still cooling and I focus out on a star test there is a triangular pattern in the test like a tri-spoke bicycle wheel overlain on the pattern. This pattern is not present when the focus is in. My intiution suggests it has something to to with the mirror clips, but the absence on the in-focus test is puzzling. When the mirror is stabilized the pattern is gone. Also, I have ordered Suiter's book but haven't received it yet so I cannot consult that tome. Any suggestions: Don't worry/loosen your clips/wait until it is cool to do a star test?

It may very well be the clips. There will be a variation in the cooling rate of the mirror at those point. And they will contribute some small thermal signal to the image as well as they cool.

I have noticed the same thing in my newts.

It is most likely the mirror clips. They not touch the mirror surface but ride about the thickness of a playing card above the mirror. They should also not fit snug against the sides and should have about the same clearance there. A good test is to grab the mirror by the edges and try to turn it in the cell. It should turn easily without binding but without any real side to side motion.