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Fireball Sightings 2010 Part 2

Observations of the December 8-9 fireball arrived from 76 places across the country, as demonstrated by the accompanying sketch map, showing most of mainland Britain. The red dots indicate sites from where reports were received, though sometimes one dot may represent several observers too close together to show separately at this scale. The red arrow gives the more probable best-estimated projected surface track for the fireball, referred to below as the "centre line", while the shaded red oval surrounding it is the area within which the meteor most likely occurred, to give an impression of the errors involved in determining the centre line. As the data available did not all confirm a single pattern for where the meteor may have been, the following discussion relies on the region and path which gave the higher probabilities only. The most certain aspect is that the fireball had a generally east to west trending trajectory above northern England. Its start point most probably occurred above County Durham, North Yorkshire, the East Riding, or the North Sea offshore of there, or perhaps parts of the adjacent English counties. The centre line looked to have begun at around 105 km altitude just inland of the North Yorkshire coast, about 7 km northwest of Scarborough (around 54.3° N, 0.4° W). The visible end was then plausibly over western North Yorkshire, western County Durham, northeast Lancashire or southeast Cumbria. Again using the centre line, an end point near 54.3° N, 2.0° W can be proposed, over northwest North Yorkshire, likely at around 60 km altitude above the eastern Pennines of upper Wensleydale near Aysgarth. Orders-of-magnitude for the errors on these positions from the centre line were at least +/-+/- 0.75° error on the geographic coordinates. Remembering the centre line was not definitive, and merely drew on what most of the reports would at least partly support, if we assume it to have been approximately correct, the projected surface path would have been ~105 km long. The fireball's atmospheric trajectory would then have descended at about 23°-24° to the horizontal (or between about 13° to 30° dependent on the error margin), giving an atmospheric path length of ~115 km (or between 108-124 km). Estimates for the object's visible flight ranged from 1 to 10 seconds, according to those who saw all or most of the event, but most (85%), including the few more experienced astronomical observers, favoured a duration of six seconds or less, the majority (68%) between 2 to 4 seconds, with an overall average for all the estimates of 3.9 seconds. Using this average with the atmospheric path lengths proposed above gave an atmospheric velocity for the meteor, not allowing for deceleration, of ~29 km/sec (error range ~28-32 km/sec), so meteorically slow. This was consistent with the relatively low start height, as slower meteors tend to ablate lower in the typical ~90-120 km altitude meteor zone. With the path direction and length, the meteor was likely a sporadic or possibly a late Northern Taurid (recent International Meteor Organization video results have indicated the Northern Taurids probably continue their activity until December 10, rather than ending in late November as had been long supposed). The path direction would have to have been much more northeast to southwest, the estimated velocity somewhat swifter, the path length greater and angled more shallowly to the horizontal for the event to have been a potential Geminid, given that that shower's radiant had barely risen to the northeast when the meteor happened. Forty-three observers commented that the object broke apart, probably in a severe fragmentation event quite late in its apparition, producing around 4 to 8 main pieces and likely a lot of smaller sparkling droplets. Ten people suggested the meteor had left a short-lived persistent train for around two seconds, though three people saw no train at all (possibly because of different local observing conditions). Colours mentioned in the main fireball included white (34%), green (20%), orange and yellow (17% each), blue (11%) and red (1%), while those in the tail or the persistent train (not everyone was clear about the distinction) were orange (27%), blue (21%), yellow and white (16% each), green or red (10% each). Nobody in the open air reported hearing any sounds associated with the meteor. The lack of acoustics and the relatively high end height counted against the possibility of any meteorites having fallen from the event, and increased the difficulty of identifying the more likely fall zone. Any solid objects continuing along the centre line would have splashed-down into the Irish Sea between the Man and Cumbrian coasts, around 20 km offshore of Maughold Head, easternmost point on the Isle of Man. The minimum potential fall zone, making allowance for the suspected errors on the meteor's estimated trajectory, but not for atmospheric effects, such as wind or drag, would have covered the Irish Sea (the largest single target) or the adjacent lands between the western end of the centre line over western England, north to southwest Scotland, west over the Isle of Man to eastern Northern Ireland and the extreme east of Eire, and south across north Wales. No fall reports from within this area were received, however. Some of the initial sightings can be found on the SPA's Observing Forum and the UK Weather World's Space Weather Forum topics for this event, with several briefer reports on a BBC News webpage , and from The Daily Telegraph online. Two video images have been located. One was on YouTube, taken from Knotty Ash near Liverpool inside a moving vehicle, but which showed probably a good part of the flight (and which was used to help refine the fireball's potential occurrence zone here). The other was caught by an automated all-sky camera run by Cambridge University, where a flash of light from the meteor occurred on the dome in shot at 17:34:14, with the tree below lit up too from the reflected flare.

2010 December 08-09 17:36 +/- 5 min. Fireball Path
2010 December 08-09 17:36 +/- 5 min. Fireball Path

The sighting of the December 9-10 near-sunset fireball was posted on December 9 by "equaitca" on the SPA's Observing Forum topic about the December 8-9 event.

Four visual sightings timed, sometimes quite imprecisely, between 20:35 and 21:00 UT later on December 9-10 indicated another multi-site fireball for southern England. The witnesses were in Oxfordshire, Hertfordshire, East Sussex and the London/Kent border, while the University of Hertfordshire's Niton camera also recorded it (the image is available on the Observing Forum topic discussing this fireball). An attempt to triangulate the reports met with only limited success. However, the fireball was plausibly over the near-coastal Pas de Calais-Flanders area of northern France to northwest Belgium, between roughly Boulogne, France to Nieuwpoort, Belgium. It may have been partly over the Channel too, probably following a path angled somewhere between south-north to southwest-northeast. For these rough paths, start heights of around 105-85 km could be suggested, though the end heights came out quite low, around 45-35 km, which may indicate the computed path was somewhat in error, particularly around its end.

The ~22:00 UT fireball on December 14-15 was reported by "Charles" (posted 2010 Dec 16) on the Observing Forum's "Geminids 2010" topic.

Alastair McBeath, SPA Meteor Section Director
Email: meteor@popastro.com
Address in Popular Astronomy

Added by:  Robin Scagell