A mass sighting of celestial phenomena or unidentified flying objects (UFO) occurred in 1561 above Nuremberg (then a Free Imperial City of the Holy Roman Empire). The phenomenon has been interpreted by some (John Keel; 'Operation Trojan Horse' p.75) modern UFO researchers as an aerial battle of extraterrestrial origin. This view is mostly dismissed by skeptics, some referencing Carl Jung's mid-twentieth century writings about the subject while others find the phenomenon is likely to be a sun dog.