60. Listen to that Shooting Star!
Image ‘borrowed’ from The Daily Telegraph website.
Some time in the 1960s. Making it one of the most ‘retro’ pages in this diary! Because it was long ago, I cannot remember any date whatsoever. But between early 1963 and 1971, we lived in a house on the north side of Birmingham, and we heard the shooting star there. Early one morning, perhaps 0100 or 0200, we were walking up the garden path after returning from a gig. The sky was quite clear. Suddenly, a long & impressive shooting star trail appeared above the line of the house roof. We had seen these before, so knew what they were; this trail was longer than average. But very strangely, it was accompanied by a sound. I can describe the sound very closely, and will do so below. But first, came my disbelief that the sound had anything to do with the shooting star. I knew well that the burning up of these tiny dust particles occurs high in the atmosphere, many miles up. A sound must certainly be generated by their combustion, as a long column of even rarified air is suddenly expanded by their incandescence. But sound only travels quite slowly, say around 1100 feet per second (~335 metres per second). So the sound would take a very long time to reach the ground – and in any case would never do so, as it would become totally attenuated after perhaps just a few miles or even less. So we could only conclude that (a) a tiny fragment of a meterorite had somehow survived practically down to ground level, and had only burnt up literally on the other side of the house; or (b) the sound we heard was produce by something else, and simply coincidentally occurred at the same time as the shooting star trail. Neither of these alternatives were particularly attractive. It was a lot quieter at 0200 even in the mid-1960s than it tends to be now. Ipso facto, where could the sound have come from? In any case, what was the sound like? It was exactly the same sound I had heard as a kid, when we had finally managed to hit a telegraph wire with a small stone from our catapult. For the sake of anybody who has never managed this feat (it was the merest fluke in my case, I assure you), it may only inadequately be described as ‘a thrumming twang’.
Anyway, the whole thing was forgotten about over the years, except at increasingly large intervals, when the memory popped up for some reason. It did so about an hour ago – 2nd December 2013. So we googled ‘can you hear a shooting star?’ And, mirabile dictu, yes, you can! For while any sound produced locally by the burn-up of a meteorite will fade away very quickly, low frequency radio waves are now known to be produced by the ionization of the air in the column of incandescence. These naturally travel at the speed of light; and under certain circumstances can be received by something on the ground which forms a kind of impromptu radio receiver – and thus be made audible. Now there were telegraph wires in that road… You see my drift? It might have been them which vibrated to some slight extent, and produced a slight ‘thrumming twang’.
That’s about it, except to remark that a burst of low frequency radio waves occurring at a height of say 40 miles (~65 Km) would be ‘broadcast’ over a very large area of the earth’s surface indeed. So ‘my’ meteorite (I think ‘meteroid’ might be the correct term these days) must have been audible, had there been an impromptu receiver to pick it up, all over the place. I wonder whether anybody else heard it? 8^) Today, there has doubtless been low frequency radio monitoring of meteor showers for a long time; still, I’m glad we were able to work it out for ourselves.
Also, the fact that radio signals transmitted from high up can be received over a very big area indeed, has given me the idea for Diary 61, which I will write as soon as I have had my dinner.
Page written 2nd December 2013.