> I was thinking maybe 3 arc-minutes (one-tenth the diameter of the moon)? Pete, Angular velocity will also be relevant. At the spatial resolution, a fast moving object will be pervieved as moving whereas a slow moving object will not. Cheers, Rob To UNSUBSCRIBE from the 'meteorobs' email list, use the Web form at: http://www.tiacdot net/users/lewkaren/meteorobs/subscribe.html