Jump to content



Photo

Can You Hear a Meteor ?

astronomy perseid meteor electromagnetic radiation vlf radio waves transducer

  • Please log in to reply
2 replies to this topic

#1 Hum

Hum

    totally wAcKed

  • 63,247 posts
  • Joined: 05-October 03
  • Location: Odder Space
  • OS: Windows XP, 7

Posted 10 August 2013 - 21:26

 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.

more




#2 arachnoid

arachnoid

    A day without sunshine is like night.

  • 4,470 posts
  • Joined: 03-November 11

Posted 10 August 2013 - 21:55

I would think it would act in the similar way to a sub sonic aircraft in that it compresses the air in front and produces a shock wave which slightly proceeds it

 

 

A shock wave is a type of propagating disturbance. Like an ordinary wave, it carries energy and can propagate through a medium (solid, liquid, gas or plasma) or in some cases in the absence of a material medium, through a field such as the electromagnetic field. Shock waves are characterized by an abrupt, nearly discontinuous change in the characteristics of the medium.[1] Across a shock there is always an extremely rapid rise in pressure, temperature and density of the flow. In supersonic flows, expansion is achieved through an expansion fan. A shock wave travels through most media at a higher speed than an ordinary wave.

http://en.wikipedia....wiki/Shock_wave



#3 zhangm

zhangm

    Just bitter.

  • 10,045 posts
  • Joined: 21-August 02

Posted 10 August 2013 - 22:01

I would think it would act in the similar way to a sub sonic aircraft in that it compresses the air in front and produces a shock wave which slightly proceeds it
 
http://en.wikipedia....wiki/Shock_wave

At the altitudes concerned, not much air, acoustic propagation to listeners at sea level should still take a noticeable amount of time. I agree with the transduction theory, since it has been shown that folks can hear auroras as well.