Twenty years later

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The first reports of the Tunguska fireball reached the Western world in 1928. The following year, C.J.P. Cave, a British astronomer, noticed the coincidence of the date of the fireball and the graphs recorded at six different locations in England on 30 June 1908. In 1930 another British astronomer, Francis John Welsh Whipple (not the American astronomer Fred Lawrence Whipple who, as we'll see, proposed the 'dirty snowball' model for comets), suggested that the airwaves in England were caused by the great Siberian meteorite, as the Tunguska fireball was known then. 'How it happened that the fall of the great meteor which produced the waves was not brought to the notice of the scientific world at the time is a mystery', he said at a meeting of the Royal Meteorological Society. 'There are many marvellous features in the story of the Siberian meteorite, a story without parallel in historical times. It is most remarkable that such an event should occur in our generation, and yet be so nearly ignored.'

Whipple used the six graphs to show that the pressure fronts had been travelling with an average speed of about 1,130 kilometres per hour. Pressure waves of similar intensity were recorded in Britain on 27 August 1883 when a volcanic eruption happened on the other side of the world, at Krakatoa on the Indonesian island of Rakata. Whipple also established that the first four 'almost similar' waves were registered within a period of two minutes, and then the final two waves followed. He concluded that there were two kinds of phenomena: the first four waves were caused by a meteorite passing through the atmosphere, and the last two waves referred to the meteorite striking the ground.

After reading Whipple's paper, another astronomer, Spencer Russell, immediately associated the remarkable night glows of 1908 with the Siberian meteorite. 'The entire northern sky on these two nights was of suffused red hue, varying from pink to an intense crimson', he recalled. 'There was a complete absence of scintillation or flickering, and no tendency for the formation of streamers, or a luminous arch, characteristic of auroral phenomena. Twilight on both of these nights was prolonged to daybreak, and there was no real darkness.'

Though they explained the cause of the phenomena observed in England, neither Whipple nor Spencer made any attempt to explain the nature of the great Siberian meteorite. This task was left to a relatively unknown young Russian scientist.

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