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METEORS:

- dust grains or fragments of Cometsor Asteroids that hit the Earth'satmosphere - if it hits the Earth's surface, it is called ameteorite.

| Encke and Taurids | Hale-Bopp| Leonids | Geminids |Sound of Meteors |

 


Here is are some images of a 15 August1999 meteor:

According to SandiaNational Laboratories in Albuquerque, the followingimages are "... from a videotape of the August 15, 1999 meteorfrom an all-sky camera located at Sandia National Laboratories inAlbuquerque. The camera views a spherical convex mirror that lookslike a chrome hub-cap, which produces a fish-eye image of the entiresky. The horizon is ringed by city lights, and north is toward theupper left. The meteor appears to the west, in the lower leftquadrant, and descends into the clouds as it lights up the entiresky. A radiometer indicates that the apparent magnitude peaked atabout -16.5, which is about thirty times as bright as the full moon.Directly beneath the fireball it may have been 300 times as bright asthe moon. Research has shown that meteoroids weighing roughly one tonget this bright when they enter the atmosphere. ...":

 


 

In 1940 Whipple discovered that the TAURIDMETEORS were fragments of COMETENCKE.


 

Could some meteorites befragments of Comet Hale-Bopp?

 

According to Skyand Telescope, the

"... Leonid shower

occurs when Earth passes near the orbit of Comet55P/Tempel-Tuttle. When the comet visits the inner solar system,the Leonid shower sometimes produces a veritable storm of meteors.This last occurred in 1966, when up to 40 meteors per second wereseen for about an hour! Both 1998 and 1999 are good years to watchfor a possible repeat of this performance. Best chances: the earlymorning hours of November 17 or 18, 1998, and November 18, 1999."

 


 According to a7 December 2001 Science@NASA web page:

"... Earth is [7 December 2001] entering the outskirts ofa dusty debris cloud shed by a mysterious object named 3200 Phaethon.It's the beginning of the annual

Geminid meteorshower,

which peaks this year [2001] on Dec. 13th and 14th. Thetwo-week long Geminid shower is barely a trickle at the moment --only 5 to 10 meteors per hour. But soon it will intensify ten-fold ormore. You can catch the main event beginning just after sunset onThursday, Dec. 13th. "When the Sun goes down on Thursday," says BillCooke of the NASA Marshall Space Flight Center, "Gemini will be lowbut rising over the eastern horizon [as viewed from mid-northernlatitudes]. You won't see many meteors then, but the ones you dowill likely be beautiful Earthgrazers" -- that is, disintegratingmeteoroids that fly over the horizon nearly parallel to theatmosphere. Earthgrazers are long, bright and vivid. A remarkablesight. ... Gemini will continue to climb higher in the sky. "Aroundmidnight go back outside," he suggests. "Gemini will lie almostdirectly overhead. From midnight until dawn on Friday, Dec. 14th,you could spot as many as 100 shooting stars per hour." ...Nowadays the Geminids are generally regarded as one of the bestannual meteor showers. But it wasn't always so. ...

... The first Geminid shower suddenly appeared in 1862,surprising sky watchers who saw 15 or so shooting stars eachhour.Astronomers immediately began looking for a comet. Most meteorshowers result from debris that that boils off a comet when it passesclose to the Sun. When Earth passes through the debris, we see ameteor shower. For more than a century astronomers searched invain for the parent of the Geminids. Finally, in 1983, NASA'sInfra-Red Astronomy Satellite (IRAS) spotted something. It wasseveral-km wide and moved in much the same orbit as the Geminidmeteoroids. Scientists named it 3200 Phaethon.

But rather than solving the puzzle of the Geminids parentage, theIRAS discovery simply deepened the mystery. Why? Because Phaethonappears to be an asteroid. Indeed it's cataloged as apotentially-hazardous one that skims by Earth's orbit only 8 timesfarther away than the Moon. Asteroids that spew debris into spacelike a comet are rare indeed, so astronomers were more baffledthan ever.

Since then many sky watchers have come to regard the Geminidsas a "weird" meteor shower -- the only one caused by anasteroid.

But maybe, says Cooke, it's not so weird after all. "I don't thinkthe Geminids come from an asteroid. They're cometary ... just likeall the other meteor showers. 3200 Phaethon is indeed the parent,but it's an extinct or dormant comet." According to Cooke,Phaethon probably looked much like other comets many centuriesago, with a fuzzy head and a glowing dusty tail. But this one wasdoomed to rapid extinction by its short-period sungrazing orbit.Every one and a half years Phaethon plunges sunward from theasteroid belt and swings by the Sun at a distance of 0.14astronomical units -- closer even than the planet Mercury. Such nearencounters with the Sun would have cooked Phaethon, vaporizing itsices and leaving behind a shell of asteroid-like dust androck.

Such over-cooked comets may be abundant, says Mike A'Hearn (Univ.of Maryland), the principal investigator of NASA's Deep Impactmission. "Dynamical studies suggest that perhaps a few percent to 50%of all near-Earth objects are dormant or extinct comets masqueradingas asteroids." From a distance there's no definitive way to tell thetwo apart. "Both comets and main belt asteroids are very dark," saysLucy McFadden (Univ. of Maryland), a member of the Deep Impactscience team. "And we don't know of any robust chemical or spectralsignature to absolutely identify a comet's nucleus." Indeed, shesays, "even if we were to fly to Phaethon we might not be able totell whether it is an extinct comet" without somehow looking beneathits crust. ...".

According to a11 December 2000 Science@NASA web page: "... Every year inmid-December when the Geminid meteor shower is active, Earth isbarely eight lunar distances (~0.021 AU) from Phaethon's orbit. Thatmakes Phaethon a "potentially hazardous" near-Earth asteroid(NEA). ...

... In July 1996 astronomers saw something in the asteroidbelt that could be relevant to the past experiences of 3200 Phaethon."Four years ago Eric Elst contacted us from the European SouthernObservatory and reported a strange object (now known as'Elst-Pizarro' after its discoverers)," recalled Marsden. "Ithad a tail, like a comet, but no coma. We calculated an orbitand it seemed to be a perfectly ordinary minor planet in the asteroidbelt. Furthermore, we found some older images of it from 1979 and'85. There was no tail in those photos and by 1997 the tail Elst sawa year earlier was gone." ... says Marsden. "We may have beenseeing a cloud of dust that was ejected by an impact with anotherasteroid or, perhaps, a small ice deposit became uncovered andvaporized." ...

... A collision between Phaethon and some smaller object in theasteroid belt might account for the Geminid debris stream. ... Thedebris trail seems to be spread rather uniformly around Phaethon'sorbit -

[ aJPL Java applet web page shows the orbit of Phaethon

as of 14 December 2001 ]

- another indicator that the meteoroids are old. ...".

 

 


Sound of Meteors

According to a 29 March 2000 article on the Space.comwebsite by Robery Roy Britt and Mary Motta: "... in the early1970s ... Chuck Bonner and his playmates heard a loud, abnormalwhistling noise accompanied by a buzz. ... they spotted a greenfireball as large as a full moon streaking across the sky. Eversince, Bonner ... has wondered how he could have heard theapparent meteor before he saw it, since sound travels much slowerthan light. ... There are only a handful of "earwitness" accountsof these melodious symphonies in the sky. One account from China in817 AD tells of a noise "like a flock of cranes in flight." A commonand curious thread in these tales is that the sound seems to travelat the speed of light ... Australian researcher Colin Keay ...developed in the early 1980s ... the theory ... [that]...when a space rock plunges earthward, friction caused by theatmosphere creates a trail of electrically charged particles, orplasma, in which Earth's invisible but potent magnetic field linesbecome trapped, tangled and twisted like strings of cooked spaghetti.This magnetic spaghetti is thought to generate very low frequencyradio waves, says Keay ... The waves are thought to travel at thespeed of light and are converted into sound when they interact nearthe ground with what are called "dielectric media" or "transducers,"which can be massive ordinary objects or electrical activity in thelower atmosphere. ...".

ColinKeay says, in a webarticle: "... the transfer of energy from a meteor fireball(bolide) to create the anomalous sounds had to be by means ofelectromagnetic radiation ... in nuclear explosions ... an intenseburst of radio emission is produced of sufficient intensity to burnout electronic equipment. Reportedly it may be heard as a "click" bysoldiers in bunkers near such a blast. ... What if the Earth'smagnetic field was ... trapped in the turbulent plasma trailbehind the bolide, and released when the plasma cooled and theionisation neutralised itself? Calculations indicated that such a"magnetic spaghetti" could arise in a turbulent bolide trail.Turbulent conditions only exist when the trail is below a certainheight in the atmosphere. And for the effect to be sustained for upto ten or more seconds the bolide must arrive in a shallowtrajectory. These restrictions provide the underlying basis forAstapovich's empirical conclusions many decades ago that only bolidesin low trajectories give rise to reports of electrophonic sounds. ...V.A. Bronshten ... endorsed the concepts in his treatise Physics ofMeteoric Phenomena, and in a paper expanding my calculations heshowed that a bolide twice as bright as a full moon could generatewell over a megawatt of radio power by my "magnetic spaghetti"process. .... At Nagoya University Dr T Watanabe showed me ... hisVLF chart recording, a radio spectrogram by Dr T Okada and thephotometry from a carefully timed fireball photograph obtained by KSuzuki and his students. ... Observational proof that large meteorsmay produce audio frequency electromagnetic radiation has given vitalsupport to the concepts ... the majority of bodies large enough toproduce sustained electrophonic sounds by travelling in shallowtrajectories are of stony composition, and an estimated 16,000 occurevery year over the entire surface of the Earth. These are closelyfollowed in numbers by the more readily fragmenting carbonaceouschondrites at 12,000 per year. Then there are the very fragile bodiesof cometary composition at 4,600 per year, and lastly the fluffy verylow density bodies also of cometary origin which come in at the rateof 1,300 per year. ... at any given location a nighttimeelectrophonic fireball may be expected about once every two or threeyears. However it is found that only between four and eight percentof witnesses of large fireballs actually hear the electrophonicsounds while the others hear nothing apart from the acousticallypropagated sonic booms and rumbles arriving minutes later. ... One ortwo people in a group may hear the sounds while others do not. Or oneentire group may report the sounds while other people in lessfavourable surroundings hear nothing. ... ".

 

 


 

  

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