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2002 October 5–6, Brilliant Bolide over Belgium and France

 

04h53m UT, October 5-6, 2002

October 4-5 and 5-6, 2002, saw three UK fireball reports to the Section, a somewhat unusual group. The first two were seen only by single witnesses however, at roughly 19h00m UT on October 4-5 from Worcestershire, and at about 01h10m UT on October 5-6 from Northumberland. The third event was much more widely-seen, at 04h53m UT +/- 1 minute on October 5-6, as spotted from places across southern England up into the Midlands, and across Belgium. It is this event we examine here.

A total of 16 sightings from England and Belgium gave some useful details on the fireball. Several other reports, mostly from media sources or unrecorded phonecalls to observatories or the emergency services, were received, but no information on the fireball's timing, appearance, or sky position could be extracted from these, only notes that the event had been seen, and sometimes a rough observer's location. The approximate locations of those observers able to provide comments concerning the object's track in the sky are indicated on the accompanying sketch map here by the red target symbols. Note that some of these represent two or more observers where the sites were too close together to show separately at this scale. The outlying four symbols (two in England, two in Belgium) clockwise from the south-western one denote sites at: Lyme Regis, Dorset; Tamworth, Staffordshire & Coventry, West Midlands; motorway between Mol and Geel, Antwerpen; and Andenne, Namur.

Best estimates for the fireball's brilliance indicated a magnitude range of -12/-15, about as bright as, or brighter than, full Moon, enough to alert observers indoors, light up the sky, or the clouds, or the ground, depending on where the observers were at the time. Two witnesses reported seeing the event begin with a bright flare, and two more commented the end-flare was spectacularly violent as well. Seven observers said fragmentation was seen along the track and near the end, and these small pieces were typically described as red in colour. The bolide itself was noted as having a blue or green colour dominant for at least part of the trail by eleven of the twelve witnesses who gave such information, though red or orange was a relatively common secondary colour mentioned (6 of the 12 colour reports). No sonic effects were reported by any of the observers, with several commenting specifically on this absence.

As no photographic or video images were secured showing the trail, and as morning twilight was underway at the time, the accuracy of the positional information on the fireball's trajectory was often poor, and only three reports gave enough data to establish the provisional projected surface track shown in the sketch map (the red arrow). The most probable best-fit approximations for the atmospheric trajectory from an analysis of these are as follows.

The start of the visible trail was at around 130 km altitude over the southern North Sea, roughly 30 km offshore north of Blankenberge, Belgium (more or less due west of the western tip of the Zeeland peninsula in the Netherlands), at ~ 51.6 degrees N, 3.1 degrees E. The visible end was at about 80 km altitude over Picardy, northern France, about 20 km ENE of Amiens, at ~ 49.9 degrees N, 2.6 degrees E. This gives a very shallow, probably near-grazing, entry angle of circa 15 degrees from the horizontal, and a visible atmospheric path length of ~195 km.

Assuming that several independent estimates for the full-trail duration of around 20-30 seconds were close to the truth, gives a mean atmospheric velocity of ~6-10 km/sec, which most likely significantly decelerated during the flight from an original, probably in the bottom end of the meteoric range, of the order of 11-15 km/sec or a little more. In the absence of detailed imaging data, which would be necessary for definite confirmation, this deceleration, and the potential problems the very low intra-atmospheric velocity may have created (for example, a possible non-rectilinear atmospheric path, due to the Earth's gravitational attraction), have been ignored. The velocity range thus established suggests the bolide was due to a natural, large, meteoroid, and was not a man-made re-entry event as had been earlier suspected.

Projecting a straight-line path along this atmospheric trajectory from the visible end point, implies a maximum-distance impact point for any surviving meteorites about 20 km north-east of Orleans, France, at ~ 48 degrees N, 2.1 degrees E, although any meteoritic fragments might have fallen earlier in the dark flight stage, some way south of Paris. No reports of any possible meteorites associated with this bolide have come to light however. The near-grazing, high-altitude, track, and the long duration and heavy fragmentation observed in the meteor ablation zone, reduce the possibility of any surviving pieces large enough to be easily found on the surface, unfortunately.

Acknowledgements

Many thanks go to all the individual observers for their sightings, and also to Clive Down and Andy Salmon of the SPA, Mike Dale of Royal Observatory Edinburgh and Mike Feist of Foredown Tower Astronomy Group for forwarding details from reports they collected. Especial thanks go to Hendrik Vandenbruaene of the Belgian VVS meteor observing group for providing summaries of all the data he received on this event, without which this analysis could not have been completed. Details on these sightings can be found on the VVS website.

Report prepared by Alastair McBeath, SPA Meteor Section Director.

Added by:  Robin Scagell