[BAA-ebulletin 00698] BRILLIANT FRAGMENTING FIREBALL OF 21 SEPTEMBER 2012

[Rick]

[BAA-ebulletin 00698] BRILLIANT FRAGMENTING FIREBALL OF 21 SEPTEMBER 2012
(c) 2012 British Astronomical Association    http://www.britastro.org/

Hundreds of eyewitness reports are coming in of a brilliant fragmenting fireball, visible at about 22:55 BST (21:55 UT) on Friday, 21st September 2012. This is clearly one of the most dramatic events reported to the BAA Meteor Section in recent years.

On Friday evening, there was scattered and more continuous cloud cover over much of South-East England, but the rest of the UK and Ireland were largely very clear, with transparent starry skies. This, coupled with the fact that many people were out on a Friday evening and the truly spectacular nature of the fireball itself, are clearly the main factors in it being reported by so many thousands of people over such a very wide area. This extends northwards and westwards from a line roughly linking Norfolk in the East to Devon in the South-West, with the majority of sightings so far received coming from Wales, the North-West, Central and North of England, Scotland and much of Ireland.

When first seen the fireball appeared as a single very brilliant object but it then fragmented into a very large number of bright secondary fireballs, all travelling along roughly parallel paths across the sky.

One highly unusual feature of this fireball is the length of time for which it was visible due to its apparent very slow speed of movement across the sky.  This has led some people to speculate that the fireball was due to the re-entry of a large fragment of space debris.  However, there are several aspects of the event, at this very early phase of the investigation, that do not appear to fit with this hypothesis and it would be unwise to rule out other possibilities at this stage.

The undersigned has received many reports of the fireball, but these extracts from the following two more detailed accounts (which have, of necessity, been shortened here) give a very good general idea of the nature of this most unusual event.

From David Stewart, Observing Coordinator of the Irish Astronomical Association (IAA), observing from Delamont Country Park, one mile south of Killyleagh in County Down.
"At 22:54 BST, a group of 12 IAA members spotted an amazing group of fireballs rising from trees at the eastern horizon to the right of Jupiter as seen from the main car park. It was immediately thought they might be fireworks but they continued to rise at a steady pace and fan out slightly as they approached us from distance with their numbers increasing and their brilliant intensity remaining unchanged. We estimated approximately 20-30 fireballs were seen following the same east to west trajectory each with an estimated brightness between mag. -5 to -7 and each left a medium trail as they travelled almost directly overhead. No noise was heard except for the excited astronomers. A larger group of 4 or 5 fireballs were at the front of the group and differences in size were apparent but each burned with a similar brightness and a distinct orange hue. We were able to observe the fireballs for 2mins from the trees in the east to the trees in western horizon and we had particularly good views in that direction. As the fireballs approached the western horizon their numbers dwindled, possibly due to burning up and atmospheric extinction, at least 2 or 3 were seen disappearing behind trees. They were travelling at a speed somewhat faster than the ISS but not as fast as a typical meteorite on entry into the Earth's atmosphere."

And from Paul Buglass, reporting on behalf of 10+ members of the York Astronomical Society (YAS) who were observing at the YAS Observatory, 4 miles west of York. Conditions were totally clear, and a very transparent night.
"At approximately 10:56ish (BST), a group of us were talking outside and I noticed a very bright light low down over York (due East), very bright with a slight green tint. It seemed to be moving very slowly, flickering slightly, and at first I thought it was a low flying aircraft, then I thought perhaps it was a helicopter.  It still hadn't moved much, but as the seconds ticked by it slowly started to show more movement to the left and slightly gain elevation .As its angular velocity increased, the bright green light started to show a slight tail as it passed through the bottom of Auriga, and then as its apparent angular speed increased more, a longer trail of darker red/orange trail formed, with bits coming off, as it approached the Plough. It then started to lose more distinct fragments downstream, with a orange almost ember like appearance, then the main bright white/green head puffed explosively and lost many more orange fragments which trailed off downstream as it passed through the Plough.. It continued West in a very flat trajectory, gradually losing the bright head as it moved to the West, and . faded to about 6 or 7 glowing orange points .  The direction it was finally lost from view was directly under Hercules.. Total observation time was possibly 60+ seconds from first sighting low in the East to fading from view in the West."

Most of the reports received so far are either quite brief or contain a lot of descriptive information about the fireball's changing visual appearance, BUT we urgently need more positional information relating to the fireball's trajectory across the night sky.  Photographs which show background stars, and even video clips or still images from mobile phones could prove very useful in this regard.

PLEASE could local society secretaries or other officers who receive this e-bulletin circulate it to all of their members and any other interested parties.

Clearly this was a very major fireball event and any BAA members who saw it, or who may have been contacted by non-astronomers who witnessed it, are asked to collect as much information about the sighting as possible and send it either to the Meteor Section Director at docjohn at dircon.co.uk or to meteor at britastro.org.

Useful information will include the name and location of the observer, the precise time of the event, the altitude and azimuth of the start and end points of the visible track, the position of the observed track against the background stars, and a description of the fireball's visual appearance, colour, etc. together with any unusual features.

This e-bulletin issued by:
John W. Mason, Director, BAA Meteor Section
2012 September 22