An April 1561 broadsheet by Hans Glaser described a mass sighting of celestial phenomena or unidentified flying objects (UFO) above Nuremberg (then a Free Imperial City of the Holy Roman Empire). Ufoologists have speculated that these phenomena may have been extraterrestrial spacecraft. Skeptics assert that the phenomenon was likely to have been another atmospheric phenomenon, such as a sun dog, although the print does not fit the usual classic description of the phenomena.