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April 6-7 2002 Fireballs

An SPA Meteor Section Special Report At least three bright fireballs occurred over western Europe on 2002 April 6-7, each reported from multiple sites. A fourth fireball over the UK was suspected around 02h30m UT, but the sole forwarded comment about this could not be confirmed, and no additional sightings of it were recovered. Another very bright fireball, but on April 7-8 at 02h55m UT, remained with just a single sighting from Fife in Scotland. Here, we take a look at the three "main events" of April 6-7.

2002 April 6-7, 20h20m18s UT

The first fireball was so very precisely timed thanks to three Czech radiometric detectors. It was very widely seen, and was photographed from seven European Fireball Network (EN) stations, each station using at least one all-sky camera, five in Germany, one in the Czech Republic and the seventh in Austria. The photographic data thus secured enabled a very accurate atmospheric trajectory to be derived, ultimately leading to an orbit determination for the original meteoroid in space. All the analysis work was carried out by experts at the EN headquarters, the Czech Ondrejov Observatory.The fireball had a visible flight nearly 92 km long, and penetrated very deeply - unusually so - into the atmosphere, before ceasing to glow, dropping at a steep angle of 49.5 degrees from the horizontal. It first became luminous at 85.6 km altitude some 15 km east-north-east of Innsbruck, Austria, heading north-west towards the Austro-German border south of Garmisch-Partenkirchen, where it reached its maximum brilliance, about magnitude -17/-18 in a flare at only 21 km altitude. Its visible flight ended above the border some 20 km west of Garmisch-Partenkirchen at just 15.8 km altitude. Its entry velocity was measured as 20.9 km/sec, but it decelerated violently during its flight, to reach an end-luminous velocity of just 4 km/sec.Such a rare, deep atmospheric penetration made a meteorite fall quite probable. Of the original ~ 500 kg, it is estimated a total of around 30 kg of fragments might have reached the surface. However, any surviving pieces will have landed in extremely difficult high Alpine terrain east of Schwangau in Germany, and so far, none have been recovered. A detailed report was issued on the IMO-News e-mailing list on April 17 by Pavel Spurny of the Ondrejov Observatory, from where many of the details here come. The IMO-News archive can be accessed through the International Meteor Organization's website at: www.imo.net Interestingly, the orbit determined was almost identical to that of the Pribram meteorite's, which fell in Czechoslovakia on 1959 April 7. The 2002 event showed characteristics typical of the Type I meteoritic fireballs, most of which are stony chondrites, which also fits, as the Pribram meteorite is an H5 chondrite.

2002 April 6-7, 00h28m UT

The second event was a magnitude -8/-12, yellow-orange brightening to green fireball. It received detailed reports from ten UK sites, plus others in Belgium and the Netherlands. The information given here is derived chiefly from the British sightings. The meteor first became visible around 120 km above the surface between Birmingham and Coventry (near 52 degrees 21' N, 1 degree 45' W), and flew north-eastwards from there, ending probably a short way out over the North Sea offshore between Skipsea and Atwick in Humberside (~ 53 degrees 57' N, 0 degrees 12' W) at about 25 km altitude. The luminous atmospheric trajectory was thus ~ 222 km long, at an angle of descent from the horizontal of some 25 degreees, giving a projected surface track about 200 km long. This is illustrated in the sketch map here, where the named cities close to the ground path are shown as open rings, while small target symbols show the locations of the ten observers. The "X" in the North Sea, roughly 40 km offshore of Scarborough, indicates the probable splashdown point for any surviving meteorites. Sonic booms were reported from the site nearest Hull around two minutes after the meteor had passed, which helps support the low visible end-point. Best-estimates for the flight time were between six to eight seconds, implying a mean atmospheric velocity, not allowing for deceleration, of ~ 32 +/- 5 km/sec.

2002 April 6-7, 03h56m UT

Three sightings from Lancashire, Cumbria and Ayrshire in Scotland of this magnitude -8 or so fireball were secured, though unfortunately, only one of the observers was able to give a reasonably accurate position for the meteor's apparent path through the sky. It has not been possible to define an accurate trajectory for this event as a result, but it probably flew on a roughly south to north track (possibly south-west to north-east) high over the Irish Sea somewhere between the Cumbrian coast and the Isle of Man.

Acknowledgements My thanks go to all the observers for their individual reports, and also to Mike Dale of Royal Observatory Edinburgh and John Lambert of Newcastle AS for their assistance in collecting many of the 00h28m UT event's reports particularly.

Alastair McBeath, SPA Meteor Section Director.

Prepared by Alastair McBeath Email: meteor@popastro.com

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