When the Perseid meteor shower bursts across the sky later this month, will people be able to hear it?
For centuries, people have reported hearing a sound made by meteors as they streaked across the skies overhead. And with the Perseids about to dazzle skywatchers with a meteor display that will earn it the title "fireball champion," some researchers are wondering if the Perseid meteor shower will be heard as well as seen.
In A.D. 817, as a meteor shower passed over China, many observers reported hearing buzzing, sizzling or hissing sounds, according to a 1992 report by Colin Keay, a physicist at the University of Newcastle in Australia.
A similar phenomenon occurred in 1719, when a fireball passed over England. Astronomer Edmond Halley reported, "Of several accidents that were reported to have attended its passage, many were the effect of pure fantasy, such as the hearing it hiss as it went along, as if it had been near at hand."
Halley (who also calculated the orbit of the eponymous Halley's Comet) was among the first to note that, if a distant meteor makes a sound, that sound should arrive after the meteor had passed, not simultaneously, since sound travels much more slowly than the speed of light.
As recently as the 1970s, people who reported hearing a sound as a meteor passed were routinely dismissed as crackpots, according to the report by Keay, published in the journal Asteroids, Comets, Meteors.
But after a large meteor passed over New South Wales in 1978, hundreds of anecdotal reports from people who claim they heard the meteor flooded the news media. Keay analyzed 36 of these reports and drew some important conclusions.
Meteors obviously release electromagnetic radiation in the visible portion of the spectrum, but the fact that they also release very low frequency (VLF) radio waves, below 30 kilohertz, is less known and less studied.
Because these VLF radio waves travel at the speed of light (not at the speed of sound), they arrive at the same time observers see a meteor passing overhead. But in order to be heard by hundreds of people, Keay deduced, radio waves need a "transducer," or some physical object that could create a sound.