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(meteorobs) [IMO-News] January 9 bolide over UK: Update
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Lew Gramer <owner-meteorobs@jovian.com>
------- Forwarded Message
Date: Sun, 13 Feb 2000 14:21:27 +0000
From: Alastair McBeath <mcbal.gwyvre@virgindot net>
To: imo-news@egroups.com
Subject: [IMO-News] January 9 bolide over UK: Update
Brilliant bolide over UK, January 9, 2000: Update
Following my previous IMO-News message concerning this event (posted
January 12), a number of further reports were received, though
unfortunately very few witnesses managed to give useful sky positions
for the visible trail. The total number of sightings now stands at 19,
from Banff in northern Scotland to Portmarnock near Dublin in Ireland,
Cardiff in Wales and near Mansfield in England at the southern limit.
Just three of these reports arrived from sites north of the track
however. The imprecise nature of many sightings means the details given
here remain regrettably tentative. Two reports of acoustic sounds heard
at roughly the correct time, but where no meteor was seen, were also
received.
The bolide occurred at around 01:56 UT on 2000 January 9. Assuming a
start height of about 90km and an end height of ~30km not inconsistent
with several reports of acoustic sounds, the fireball's visible track
probably started above or not far from Appleby in Cumbria (54d35'N,
2d30'W), and ended roughly 10+ km offshore due east of Seaton Sluice,
Northumberland (55d05'N, 1d15'W). The trajectory probably passed
directly over part of the conurbations of Newcastle and Gateshead. It
was seen as "almost overhead" from a site on the western outskirts of
Sunderland, probably only ~12km south of the proposed ground track, for
instance. The trajectory would have passed at an elevation of ~73d
(range ~70d-75d) for the observers here, a reasonable lay-estimate for
"almost overhead". The ends of this track could be extended
west/south-west (start), or east/north-east (end) of these places, plus
the track could be shifted somewhat north or south of this current one,
but all the sightings received can be fitted to this pattern. The ground
track (including the part over the North Sea) would thus have been
around 90 km, trending south-west to north-east. Splashdown for any
meteorites would have been well out into the North Sea, maybe 40-60+ km
from land.
The atmospheric trajectory of the object based on the above ground track
gives an angle of descent from the horizontal of about 33d (uncertainty
~30d-35d), and an atmospheric path length of about 110 km. Assuming this
was completed in ~5 seconds (in-line with the more accurate reports),
this equates with a mean atmospheric velocity not allowing for
deceleration of 22 km/sec (range perhaps ~20-25 km/sec). Distinct late
deceleration was a factor mentioned in a couple of reports that were
almost perpendicular to the trail, but in the absence of photos or
videos, this was not sensibly determinable.
Acoustic reports were received from several locations, which have been
further used to support the line of the track above, based on the usual
values for sound in air at mean sea level. Two reports from Morpeth in
Northumberland were from people who were awoken shortly before 02:00 UT
by loud noises like an explosion or nearby thunder. Morpeth would have
been about 30km north-west of the proposed end-point. The fact that the
night was clear and still, and the hour far too late for low-level
military or civilian jet aircraft flights was commented upon in both
instances. An additional acoustic sound report came from the Banff
observer, who would have been about 280km from the meteor's end point.
The sound should have taken around 13-15 minutes to arrive, but no
estimate of the time delay could be given. This might seem a long
distance for sound to persist, but it would have passed largely over
water on a night noted by several observers as being very calm.
A single report of possible electrophonic sounds simultaneous with the
meteor's flight was received from Eston Nab (54d33.5'N, 1d07'W), a hill
perhaps ~60km south-east of the ground track at its closest. These were
described as "Whoosh, then rustling".
A persistent train lasting for several seconds occurred, and the meteor
seems to have been fragmenting along part of its later stages at least.
The colours were generally given as green-yellow or green-white, with
red or orange-red sparks/fragments. Three main fragments were reported
by several witnesses as falling near the end of the visible flight.
As for its brightness, this was perhaps between magnitudes -15 to -20 or
so. "Brighter than full Moon" was the most accurate measure any witness
suggested, but the event lit up the sky and cast clear, moving shadows
for some observers at least.
I am very grateful to Ray Worthy of Cleveland & Darlington AS (who
rounded up reports from south of the River Tyne), John Lambert of
Newcastle AS (who endeavoured to do the same north of the Tyne) and Mike
Dale of Royal Observatory Edinburgh, for all their assistance in
tracking down and forwarding most of the reports on this object, and to
all the observers who contributed information.
Alastair McBeath,
SPA Meteor Section Director.
E-mail: vice_president@imodot net
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