a comet is a kind of celestial object
celestial_object is astronomical_object. periodic_comet is comet. comet is extraterrestrial_object. comet is not extraterrestrial_object. celestial_object is not celestial_object. celestial_object is heavenly_body. celestial_object is celestial_object. comet is astronomical_object. comet is not astronomical_object. constellation is celestial_object.