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2012 March 03 Fireball

(This analysis by Alastair McBeath of the widely seen UK fireball, which was visible at approx 21:41UT on 2012 March 03, originally appeared on the SPA Forum)

The final analysis of this fireball has taken rather longer than I'd anticipated, largely because of the substantial number of reports received on it, including many comments extracted from the BBC News webpage at: 

www.bbc.co.uk/news/world-17248959

161 fully detailed observations from the American Meteor Society - see their website at: 

www.amsmeteors.org/fireball2/public.php

and the summary page:

www.amsmeteors.org/2012/03/fireball-over-the-united-kingdom-march-3-2012/ 

as well as notes from Twitter. I'm especially grateful to Bob Lunsford and Mike Hankey of the AMS for alerting me to the huge number of reports they had been sent, and for making those sightings freely available to me, and to (then) Assistant SPA Meteor Director Tony Markham for rounding-up the Twitter details. 

Excluding duplicates, a total of 376 reports, including 15 videos or images of part of the trail, were probably of this event, stretching from Wick and the island of Lewis in northern Scotland to Somerset, Hampshire and Essex in southern England, with several sightings from northeast Wales. Of the 353 observers whose locations could be identified, 116 were in Scotland, 168 in northern England (north of roughly 53° N latitude, somewhat variable to allow for county boundaries), 9 in Wales, and 60 in southern England. 

It has been difficult to confirm some of the reports due to differences in the estimated timings, and where in the sky the object was claimed to have been seen. Outlying suggestions for the time of what was plausibly this fireball ranged from 21:00 to 22:30 UT, for instance! However, 80% fell within ten minutes of 21:41:30 UT on March 3, while the fireball most probably happened between 21:41 and 21:42 UT. The longevity of its flight, likely around 45 ± 15 seconds, meant the timing could not be more precisely-determined. A further complication has been that there were at least four, and possibly five, separate fireballs spotted from UK locations overnight on March 3-4.These are discussed elsewhere on the Observing Forum: 

www.popastro.com/phpBB2/viewtopic.php

The preliminary estimate for the meteor's trajectory given earlier has scarcely changed at all. The most plausible start area remains vaguely-defined as between the Faeroe, Shetland and Orkney Islands, perhaps within 100 km of 3.9° W, 60.5° N, assuming a start height range between 140-90 km, but it may have been some way west or north of this zone. The end area was more closely-confined to within 25 km of 0°45.3' W, 52°13.3' N, with a best-estimated average for its final visible height of 61.6 ± 8.5 km. As noted before, the centre of this zone on the ground was close to Bozeat, Northants, near the Northants-Beds-Bucks border.

Using this relatively fixed end-point with the data from those observers who suggested the meteor had passed overhead, or very nearly so (and excluding a few outliers), would imply the meteor's direction of travel across the British Isles was towards azimuths 165° to 170°, so moving NNW to SSE. There was a small majority in favour of the ~170° line, which would have been above the surface track described previously - so, Orkney Mainland - Duncansby Head - Moray Firth - Banff - Inverbervie - North Sea off the Firth of Forth - near Lindisfarne, then passing overhead for Newcastle, Gateshead and Durham, as well as almost so for York, Leeds, Sheffield, Nottingham and Leicester. 

Other details derived from this estimated flight-path were chiefly unchanged too, such as its intra-atmospheric trajectory being from 1060 to 900 km long, descending at between 5° to 2° from the horizontal. The larger range for its potential visible flight time, 30-60 seconds, did alter the possible atmospheric velocity range though, which would then have been circa 25 ± 10 km/sec, with no allowance for atmospheric deceleration. 

An unusually large range of estimated brightnesses were suggested from magnitude -1 to brighter than the Sun (magnitude -27), although as no one reported any serious eye problems after viewing the meteor, the more extreme brightness estimates seemed more likely a result of the surprise at seeing such an amazing meteor, rather than its actual brilliance. The more reliable estimates averaged magnitude -12 or so, with the likely brightest parts of the trail probably falling in the range from magnitude -9 to -15, roughly of half to full Moon level. The object seemed to have been about at its brightest during its passage between approximately Aberdeenshire to North Yorkshire, and judging by the descriptions (albeit with an unavoidable degree of subjectivity, as not everyone agreed what happened) it may have begun breaking up or shedding small sparkling fragments from about the time it crossed the Northumberland coast onwards, or perhaps a little before then. The degree of fragmentation overall seemed relatively slight and fairly gentle however, with people often reporting a train or tail with and/or after the meteor. There was also a degree of confusion for some people about the difference between the persistent train left after the meteor had gone, and the tail seen behind the head of the meteor while still in-flight, making determining just what took place quite difficult. Some of the videos certainly would support an amount of minor fragmentation during the later flight. 

Sounds potentially associated with the fireball were reported from seventeen places, twelve of those simultaneous with the meteor's flight or almost so, five some time afterwards. The simultaneous sounds were mostly of the kind expected from previous events of this kind, described here as often quite faint, but distinct rustling, hissing, sizzling, crackling or popping. Two witnesses, one each in Derby and Wolverhampton had their attention drawn to the fireball by hearing the sound, which has also occurred before. One report from Dumfries & Galloway (the most distant place from the projected surface track to have reported a sound associated with the meteor) suggested a boom was heard a couple of seconds after the meteor vanished, much too soon for ordinary acoustic waves to have arrived at that site, but which might still have been linked to the event, although a more earthly explanation could not be ruled-out. Another witness in Manchester mentioned sounds like the whirring and banging from a helicopter were noted during the meteor's appearance. Again, a man-made cause nearby could not be excluded. Four reports of simultaneous sounds were from Northumberland and the Borders almost directly beneath the probable line-of-flight, which provided further support for such a trajectory, with eight of the twelve within 70 km of that projected ground line. 

Of the five reports of sounds after the meteor ended, two were of sonic booms from unidentified locations (one possibly in either Derbyshire or Staffordshire), and another was of a similar boom from Worksop in Notts between 60-120 seconds after the meteor vanished, another place almost directly beneath the flight-path. The remaining two reports from Glasgow, of a double shotgun-like detonation an unknown time after the meteor disappeared, and Preston in Lancs, of a rumbling noise barely audible above the local traffic about ten minutes after the meteor, seemed more likely to have had a local cause. Whether any of these delayed noises were genuinely linked to the meteor was uncertain, since assuming the fireball's estimated trajectory was correct, it would likely have been too high to have generated such noises audibly at the surface. 

As for the colours seen in the meteor, various contrasting shades were mentioned, with some people differentiating between hues noticed in the head and tail at times. Of those who reported colours in the head, most preferred red, orange or yellow (65.5%) or white (24%) with the remaining 10.5% made up of green, blue or violet. 

Many thanks once more to all the contributing observers in sharing their good fortune at spotting such a marvellous, unusually persistent fireball. Man-made re-entry fireballs, which may last up to a few minutes, can be quite similar, and are relatively commoner. However, such naturally-occurring meteors skimming the meteor layer and lasting for tens of seconds are extremely rare, perhaps no more than a handful per century visible for any given place on Earth. Those who saw this one can thus count themselves particularly lucky! 

Alastair McBeath

Added by:  Tracie Heywood