Ball lightning is an unexplained atmospheric electrical phenomenon. The term refers to reports of luminous, spherical objects that vary from pea-sized to several meters in diameter. Though usually associated with thunderstorms, the phenomenon lasts considerably longer than the split-second flash of a lightning bolt. Many early reports claim that the ball eventually explodes, sometimes with fatal consequences, leaving behind the odor of sulfur.
Until the 1960s, most scientists treated reports of ball lightning skeptically, despite numerous accounts from around the world. Laboratory experiments can produce effects that are visually similar to reports of ball lightning, but how these relate to the natural phenomenon remains unclear.
Scientists have proposed many hypotheses about ball lightning over the centuries. Scientific data on natural ball lightning are scarce, owing to its infrequency and unpredictability. The presumption of its existence depends on reported public sightings, and has therefore produced somewhat inconsistent findings. Owing to inconsistencies and to the lack of reliable data, the true nature of ball lightning remains 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.