The Great New South Wales Fireball

The Great New South Wales Fireball

The entry into the atmosphere of a large (but not too large!) meteor fireball, or bolide, is one of the most awesome natural phenomena that a human being may witness without being greatly endangered. They are very rare events, occurring about once every fifty years at any given location, and few people ever see one during their entire lifetime. For around ten percent of those who strike it lucky the mental impression is heightened by hearing strange electrophonic sounds accompanying the event.
Such was the case when a bolide turned night into day in the skies above the cities of Sydney and Newcastle in the State of New South Wales, Australia, on April 7, 1978. It burst into view from the southwest at 4.44 am AEST on a moonless night, ninety minutes before sunrise. Its magnitude was around -16, or in other words about forty times brighter than a full moon. Observations from the Newcastle region indicated that any resulting meteorite would have fallen into the sea, but by the time that conclusion emerged the many clear reports of simultaneous hissing, rushing, swishing and crackling sounds had captured my interest. Some of the witnesses heard sounds only when the bolide flared or exploded. Others heard sounds from shortly before the time of the explosions until the light of the bolide was finally extinguished about ten seconds or more later. The fireball was luminous for upwards of twenty seconds, with its greatest brilliance commencing at the time of several explosive fragmentations about midway along its trajectory.
The following six sample reports are arranged in order of locations along the ground track of the fireball:
"Heard a noise like an express train or bus travelling at high speed. Next an electrical crackling sound, then our backyard was as light as day." A. Hayes, Edgecliff.
"A noise could be heard. A low moaning, swooshing transcribable on a tape recorder. It lasted 2 or 3 seconds." R. Williams, Willoughby.
"I heard a sound like an approaching vehicle and saw a flash of light as everything was lit up like daylight." J. Ireland, Vales Point.
"It was a loud swishing noise" J. Wright, Swansea.
"..heard a noise like a `phut' or `shower cracker' at the time of the flare. It was not loud enough to wake anyone." N. Jones, Kotara. (Mrs Jones' friend standing nearby heard nothing!)
"I heard a sound like steam hissing out of a railway engine for a count of about ten." H Drayton, Hawks Nest.
Those and other reports convinced me that there had to be some physical explanation for the sounds, regardless of their apparent inconsistencies and the problems already mentioned.
During the next fifteen months I gathered literature on the subject, consulted with fellow meteor scientists (most of whom warned me I was wasting my time) and began to critically assess the situation. I formed only one firm conclusion: the energy had to be transmitted by electromagnetic means. The other three known fundamental physical forces were unable to do so. Yet no meteor fireball had ever been found to generate its own radiation anywhere in the radio region of the electromagnetic spectrum. Excitation of sounds by heat and light was soon ruled out creating a real dilemma which required extensive scientific detective work to resolve.
The solution came gradually, assisted by the splendid research facilities available to me at the Herzberg Institute of Astrophysics run by the Canadian National Research Council in Ottawa, whose hospitality I gratefully acknowledge along with that of my host, Dr Bruce A McIntosh.