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[EPFL] [University of Kentucky]
[The International Meteor Organization]
read more: Electrophonic sounds - introduction
read more: Electrophonic sounds - existing catalogs
Electrophonic sounds:
/History/
Reports of strange noises heard simultaneously with the passage of a
bright fireball have a long history. Without doubt, some are even hidden
in very old Sumerian, Arab and Chinese chronicles. For example, a
Chinese record from the year 817 about the meteor ``which made a noise
like a flock of cranes in flight'' [12 ],
or an Arab record of a meteor shower in the year 1026, probably
Perseids, which had meteors with ``a loud sound and intense light'',
(see the record 19 in [13 ]). As soon as
the first scientific magazines appeared, such observations were
regularly recorded in them.
A Mystery of Meteors in the 18^th Century
Sir Edmund Halley At the beginning of 18^th century, sir Edmund Halley
dismissed the electrophonic sounds by interpreting them as imagination
of observers [14 ,15
]. In his letter to the Royal Society of
London in 1714 [14 ], he describes
several bright meteors visible over Europe in previous years and derives
their heights from witness reports at widely separated locations. He
obtained heights of several tens of miles, which suggests that a sound
from a meteor can not be heard simultaneously with the meteor's
appearance. He also quotes Italian astronomer /Geminian Montanari /from
Bolonia, who derived similar result for a bright meteor in 1676 over Italy:
"/..famous Meteor which was seen to pass over Italy, on the 21st. of
March O.S.Anno 1676, ... its perpendicular Altitude was at least 38
Miles: That in all Places near this Course, it was heard to make a
hissing Noise as it passed, ... it was heard to give a very great Blow,
(Tuono di maggior rumore di gross Cannonata), immediately after which,
another sort of Sound was heard, like the rattling of a great Cart
running over Stones, which continued about the time of a Credo. ... it
cannot be wonder'd that so great a Body moving with such an incredible
Velocity thro' the Air, tho' so much rarefied as it is in its upper
Regions, should occasion so great a hissing Noise, as be heard as such a
Distance as this was./"
A few years later, Halley had the opportunity to apply the same analysis
on a bright meteor over England in March of 1719 [15
]. The large height and velocity of the
meteor completely excluded the reality of "hissing" sounds which
accompanied the meteor:
"/Of several Accidents that were reported to have attended its Passage,
many were the Effect of Fancy, such as the hearing it hiss as it went
along, as if it had been very near at hand: Others imagin'd they felt
the Warmth of its Beams, and some there were that thought, at least
wrote, that they were scalded by it./"
Sir Charles Blagden's Letter
At that time, the origin of meteors was unknown , and Aristotel's view
of meteors as atmospheric phenomena was generally accepted. Intrigued
by reports of instantaneous "hissing" sounds from a large meteor on
August 18, 1783, Sir Charles Blagden is presenting his arguments for
"/electric origin of meteors/"[16 ] in
1784. Since the nature of electricity was still not understood, he
describes meteors as ``electricity fluid". In this picture, there is a
possibility for this fluid to travel faster then sound and produce
"hissing" sounds around an observer:
"/Various electrical phenomena have been seen attending meteors. Lambent
flames are described as settling upon men, horses, and other objects,
and sparks coming from them, or the whole meteor itself, it is said,
have damaged ships, houses, etc. in the manner of lightning. These
facts, I must own, are but obscurely related, yet still they do not seem
to be destitute of foundation. If there be realy any hissing noise heard
while meteors are passing, it seems explicable on no other supposition
then that of streams of electric matter issuing from them, and reaching
the earth with a velocity equal to that of the meteor, namely, in two or
three seconds. Accordingly, in one of our late meteors, the hissing was
compared to that of electricity issuing from a conductor. The sparks
flying off so perpetually from the body of fire-balls, may possibly have
some connection with these streams. In the same manner the sound of
explosions may perhaps be brought to us quicker, then if it were
propageted through the whole distance by air alone./"
Although his description of meteors was incorrect, he correctly assumed
that the instantaneous sounds are of electrical origin. It is
interesting that he compares these sounds with the aurora sounds and
derives the height of aurora to be even higher than meteors. Thus we can
say that this is also the first attempt of explaining both type of
sounds with the same theory.
Understanding of the Meteors in the 19^th Century
The Leonids in 1833A real breakthrough in understanding the origin of
meteors happened after the great Leonid meteor storm in 1833. From an
extensive collection of witness reports, Denison Olmsted derived heights
and trajectories of the meteors and rightly concluded that meteors are
low density objects from space that burn-out high in the atmosphere [18
]. He also gave a very detailed summary
of reports from many witnesses of instantaneous sounds, some of whom
were scientifically trained, and discusses the results of their
electrical and magnetic experiments [17
]. These crude experiments did not
reveal any certain change in the magnetic field of the Earth, but many
electrical anomalies were positively recorded.
"./..No change was noticeable in the magnetic dip, variation or
intensity. Gold leaf electrometers were excited by a touch, Bennett's,
placed on the prime conductor, with the cushion insulated, rose on a
slight motion of the machine. The pendulum of was
accelerated/."
"/Mr.Palmer, considering the phenomenon as electrical, immediately made
some experiments to ascertain the electrical state of the atmosphere.
His silk pocket-handkerchief held at one end in the right hand and drawn
swiftly through his left hand, emitted a very unusual number of electric
sparks. On turning a small machine, he found the sparks which were
usually short and feeble, much longer and more intense then he had ever
seen before. On presenting silk threads to an iron bar that stood on the
ground leaning against the house, they were strongly attracted towards
the iron. He next examined his compas; found the needle more unsteady
then ordinary, but on adjusting it to the meridian as nearly as he
could, judged the declination of the needle to be the same as usual./"
"/He heard at different times a number of slight explosions, which
usually resembled the noise of a child's pop-gun, and was not unlike
that of a fire-rocket. They were followed by a particular odor observed
by all the company, (four men) which one compared to the smell of
sulphur, and another to that of onions. The meteors which afforded these
sounds, all passed along in a north-west direction.... They passed below
the tops of the trees at the distance of twenty five rods from the place
where he stood, giving a "pop" just before they reached the trees. One
appeared to strike the barn, and gave a louder pop then any of the
others. An auroral light resembling day-break, appeared constantly in
the east from the time when his observations commenced./"
Since the Olmsted's calculations excluded the electric origin of
meteors, these instantaneous, (anomalous), sounds were dismissed also
and disappeared from the scientific publications later on, even though
Olmsted did not exclude their existence:
"/Meteors which were distinguished for their brightness and apparent
magnitude, and which would therefore be expected to afford sounds, might
stil be too distant for such sounds to be audible; or might be in a
region of the atmosphere where/ /the air is too much rarefied for the
purpose of sound./
/.../
/The question whether any sounds proceeded from the meteor, must rest,
for its decision, on the circumstances of the case; such as the
peculiarity of the sounds, their nature as described by different
observers, etc./"
Revival of the Anomalous Meteor Sounds at the end of the 20^th Century
The Electrophonic Sound Produced by Electrical StimulationThe term
/electrophonic sound /was introduced by S.S. Stevens in 1937 for
sensation of a sound caused by electrical current through the head[19
]. A few years later, in 1940, the name
/electrophonic bolide/ was introduced by P. Dravert as a description of
a bright meteor accompanied by, (anomalous), sound [20
]. Although the existence of electrophonic
sounds from meteors was generally ignored or dismissed as the
imagination of observers, there were attempts by some authors to rise
the problem of the origin of these sounds. For example, in 1917, J.A.
Udden [35 ] proposed dissipation of the
ether waves into sound waves "./.. on objects attached to the earth,
such as plants or artificial structures./"
The idea that radio, (ether), waves can be produced by meteors was
checked for the first time experimentally by A.G. Kalashnikov in 1949
[21 ]. He reported the detection of ULF
pulses, (at frequency of 1 Hz), coincident with meteors, but this
remained a controversial result as other authors performed similar
experiments during the 1950's [22 ,23
,24 ,25
].
During that time, the first catalogs of electrophonic sounds appeared
[26 ,27 ,28
]. The most influential was the RAND
Corporation report made by M.Romig and D.Lamar [28
], which was widely accepted in the West as
the last word on this subject. In Russia some work continued, mostly
theoretical, usually inspired by the mystery of Tuguska explosion in 1908.
ELF/VLF from a MeteorThe situation finally started to change in 1980,
when C.S.L. Keay presents the theory that meteors can emit the ELF/VLF
radio waves [2 ]. According to his
laboratory experiments, these electromagnetic waves can be transformed
into sound on ordinary objects around the observer. The ELF/VLF
radiation [4 ] would be produced by trapping
and tangling Earth's magnetic field in the turbulent plasma tail of an
ablating meteoroid. Soon after, using this theory, Bronshten gave
theoretical prediction that a meteor with minimal brightness of -12^m ,
(about equal to the brightness of a full Moon) is necessary for
production of electrophonic sounds [3 ].
Since then the interest for electrophonic sounds has been rising. New
catalogs were introduced [29 ,30
,31 ], and
extensive statistical analysis of catalogs of electrophonic sounds was
presented by Kaznev in 1994 [10 ]. His
results show a variety of electrophonic sound properties, and clearly
show that the lover brightness limit of -12^m is not realistic. Keay
refined his theory in 1992 and predicted that VLF can be generated in
the moment of the explosive disintegration of a bright bolide, and also
a little bit earlier [8 ]. Nevertheless,
this still requires slow meteors ablating at low altitudes, while some
electrophonic bolides are clearly very fast and ablating at high
altitudes, (Leonids, for example).
In 1991, Bronshten gave a very valuable overview of the vital facts and
existing theories, (mostly Russian), about electrophonic sounds [32
] and/or mechanisms for VLF emission from
meteors. His conclusion is that all proposed theories are too simplified
to be able to give the right answers and future detailed numerical
modeling of the kinetic plasma theory equations may give more precise
results.
Recently, a new theory of Electrophonic Bursters was presented by M.
Beech and L. Foschini [9 ] but it also has
difficulties like the other theories.
In the meantime, a few reports of detected ELF/VLF radiation from
meteors have been presented [6 ,7
][33 ][34
] but a much larger sample is needed for
more definite conclusions about the physics of these radio emissions
from meteors. Finally, during the 1998 Leonid meteor shower, the first
instrumental detection of electrophonic sound was obtained [34
].
Nevertheless, the phenomenon of electrophonic sounds from meteors is
still mysterious. It is not clear how the meteors can produce such a
strong ELF/VLF emission and what kind of observational conditions are
necessary for detection of these sounds. Thus the witness reports are
very valuable source of information.
/Copyright 1999 Zeljko Andreic, Dejan Vinkovic/
* Read about more recent developments in the ILWCRO press release
regarding the first instrumental detection of electrophonic meteors:
fizika.org/ilwcro/results *
read more: Electrophonic sounds - introduction
read more: Electrophonic sounds - existing catalogs
*Other sources of information about the electrophonic sound:*
*Colin Keay's Home Page *
*Phil Bagnall's Home Page *
------------------------------------------------------------------------
Dejan Vinkovic (University of Kentucky
)