Ball lightning is an unexplained atmospheric electrical phenomenon. The term refers to reports of luminous, spherical objects which vary in diameter from pea-sized to several meters. It is usually associated with thunderstorms, but lasts considerably longer than the split-second flash of a lightning bolt. Many early reports say that the ball eventually explodes, sometimes with fatal consequences, leaving behind the odor of sulfur.Until the 1960s, most scientists argued that ball lightning was not a real phenomenon but an urban myth, despite numerous reports throughout the world. Laboratory experiments can produce effects that are visually similar to reports of ball lightning, but whether these are related to the natural phenomenon remains unclear.Many scientific hypotheses about ball lightning have been proposed over the centuries. Scientific data on natural ball lightning are scarce, owing to its infrequency and unpredictability. The presumption of its existence is based on reported public sightings, and has therefore produced somewhat inconsistent findings. Given inconsistencies and lack of reliable data, the true nature of ball lightning is still unknown. The first ever optical spectrum of what appears to have been a ball lightning event was published in January 2014 and included a video at high frame rate.