737-700 horizontal stabalizer question
Last week while on a SWA flight from KHOU to KLAS, I had a window seat a few rows behind the wing. This was an early morning flight, flying more or less from east to west. The sun evidently was at such an angle, that it cast a shadow on the wing from the horizontal stablator. Had to be the horizontal, as the length of it was proportianal to the actual size. Now here's my question: We encountered "rapid intermittent chop". During this event, I noticed that the shadow would move forward and backward upon the wing, quite rapidly. What was happening back there on the tail? Was the stablator actually 'flexing' during the 'chop', or could it have been 'stablizer trim' moving the stablator rapidly?---- thanks ahead