https://www.physicsforums.com/showthread.php?p=3577768#post3577768" has caused me to question my assumptions. If a target of observation is moving at relativistic velocities but its distance does not change wrt the observer, is it observed to be experiencing time dilation? Alice stands at North Pole. Bob zooms around equator in a tight circle at .9c. Do they observe dilation in each other? I guess this gets into the non-inertial frame of reference aspect of SR.