|Help and Advice|
|Transit of Mercury 2016|
|Giving long exposures on a digital camera|
|Photographing star trails|
|Predicting the ISS and other satellites|
|Using a mirror to view a partial eclipse|
|Simple Guide to Viewing the Space Station|
|Choosing a Telescope|
|Tips when projecting the Sun|
|Starting to Use Your Telescope|
|Imaging with a DSLR through the telescope|
|Buying a telescope for a child|
|Photographing a partial eclipse|
This spectacular, long duration, slow moving fireball was visible over much of the UK (and further afield) shortly before 11pm BST on the evening of Friday 21st September 2012.
Alastair McBeath has now been able to carry out a more detailed analysis of the fireball:
* Reports: The total number of separate reports I've collected (including videos, images and visual sightings) comes to 990. Forty of these included videos or images. Ninety-one reports were from sites which could not be located, either because the witness provided insufficient, or only ambiguous, information ("Holywell" is not a single location, people...).
* Occurrence Time: From the Norway imaging evidence and details from the Netherlands, the fireball probably began at 21:55 UT over northern Germany. Assuming the visible trail lasted between two to three minutes would mean it likely crossed Britain and Ireland around 21:56-21:57 or so. However, the timing estimates by the observers were often far from this, with many failing even to give a BST or UT notation, where that would have been appropriate. The AMS reports especially featured all manner of American time zone abbreviations despite being made from Britain and nearby. In compiling the data, I assumed where possible the times were meant to be around 21:55 UT. There were obvious problems in doing so, and the overall range of timings converted to UT from what was claimed as BST ran from 19:15 to 00:10 UT for what, judging by the descriptions, must have been the same fireball. The mean from all of these was 21:58.3 UT (920 estimates), with 84% falling within ten minutes of 21:58, and 72% within five minutes of it. Given the longevity of the event, this may more closely represent the estimated end time for the fireball, rather than its start.
* Visible Duration: Many observers (675) provided estimates for how long they were able to see the event. These ranged from 2 to 300 seconds, the latter almost certainly an exaggeration. The average from all was 18.9 sec. All the observers clearly saw only part of the trail, and while this mean duration may say more for the individual's limited view of the sky, it may also provide a crude ball-park figure relating to the readily-visible interval during which the meteor passed across the British Isles. Most reported estimates (83%) fell between 10 to 60 seconds, 76% within 10 to 30 s. Just 9 reports favoured a visible time of over sixty seconds.
* Estimated Magnitude: Many people only made comparison with the Moon or Venus, with the AMS reports and those from the Lunar Meteorite Hunter blog especially favouring such comparisons. A substantial number (unrecorded) claimed the event had been of Sun-like or greater brilliance. As there were no reports of blindness, temporary or otherwise, and taking into account the generally normal video and image recordings, such extremes were discounted from further analysis. In general, I assumed a conservative brightness level where leeway was available. For example, given that the waxing crescent Moon had been readily visible in the evening sky up to a couple of hours before the meteor occurred, I assumed any comparison with the Moon meant the crescent Moon that evening, unless otherwise indicated. A further problem was that the fireball had broken up into multiple pieces during its passage over Britain, so it was not always clear exactly what people were estimating the brightness of. However, from 381 surviving estimates, a mean magnitude of -9.7 was derived, the range overall from -2 to -15 (all "brighter than full Moon" estimates which made no mention of the Sun went into the -15 bin). From the more experienced descriptions, I would suggest a range from magnitude -8 to -11 would cover the probable brilliance of the object(s) as observed.
* Colours: For what it's worth... A total of 1374 colour estimates were made (most people described more than one colour as present in some part of the event), with the division as follows: Red = 10%, Orange = 32%, Yellow = 17%, Green = 14%, Blue + Violet = 3%, White = 24%.
* Derived Angular Velocities: I extracted information from those reports where details had been provided on the first and last points of the visible trail observed, and where an estimate had been made for how long the object had remained visible, in hopes of determining angular velocities for different parts of the visible trail. Unfortunately, only 23 reports included all this information, which after computation gave a range from 0.1 to 18.7, and a mean of 5.4, degrees per second. Most (74%) fell in the range from 1.5 to 9.5 degrees per second (mean 4.6), with 52% in the 2.5 to 8.5 °/s range (mean 5.1). Despite this, as only one of these observations was made from Ireland, this may give a ball-park range of values for the apparent angular velocity as the meteor passed over mainland England.
* Estimated Trajectory Across the British Isles: (see www.popastro.com/meteor/reports/report.php for a map). Analysing reports from 66 identifiable locations of where the meteor was claimed as having passed overhead, or almost so, using the usual methods of ignoring extreme outliers and attempting to reconcile as many of the remaining sightings as possible, a central-line surface track for the estimated overhead-flight line was determined. It seems likely that the actual ground track probably fell within approximately fifteen kilometres of this line, as a best-estimate. Moving east to west with the meteor, the following identifying points can be listed:
1) Crossed the English North Sea coast just north of Scarborough town centre, and passed over the southern extent of the (northwest-)adjacent village of Scalby, North Yorkshire, around 0.39°W, 54.3°N;
2) Passed overhead at Northallerton, North Yorkshire and Windermere, Cumbria;
3) Crossed the English Irish Sea coast west of a point immediately south of Sellafield railway station, Cumbria, circa 3.5°W, 54.4°N;
4) Passed about one kilometre offshore to the north of Point of Ayre, off the Isle of Man;
5) Crossed the Northern Ireland Irish Sea coast at Cloghy (about 2.5 km south of Portavogie) on the Ards Peninsula, County Down, at about 5.45°W, 54.44°N;
6) Crossed over Strangford Lough at Ardkeen (east shore of Lough);
7) Passed overhead almost exactly midway between Lurgan and Craigavon, County Down;
8) Passed overhead at Ballygawley, County Tyrone;
9) Passed above the neck of the narrows of Lower Lough Erne, County Fermanagh, and the middle of Lough Melvin at the Counties Fermanagh-Leitrim (also Northern Ireland-Ireland) border;
10) Crossed the Atlantic coast of Ireland west of Cliffony, County Sligo, approximately 8.47°W, 54.43°N;
11) Passed overhead of Inishmurray, about 12 km offshore of the Sligo coast.
* End of Visible Flight: I extracted data from those visual observers who gave numerical end point estimates where the altitude was 10° or less only, in the hopes of determining the possible end point for the visible trajectory from the British Isles. Regrettably, only eleven such reports could be found with identifiable locations, and of those, it was apparent that just three fell even close to identifying a point off the central-western Irish Atlantic coast. These three were Leeds in England (az. 269°, alt. 0°), Waterloo, Perthshire in Scotland (az. 250°, alt. 10°) and Birdhill, County Tipperary in Ireland (az. 281°, alt. 10°). Given the problems in analysing small-angle altitudes, I used only the azimuths to determine a possible end-point bearing, and found that curiously, as far as my simple graphical map-plotting suggested, these three bearings came within about 40 km of crossing with one another near 15.6°W, 53.6°N, roughly 360 km offshore of Achil Head, Achil Island, County Mayo, Ireland! While quite a surprise, I think it would be best to treat this result with considerable caution, but it may perhaps serve as a temporary benchmark until more data from the trajectory calculations are available.
* Electrophonics: Curiously, all the reports of electrophonics in England and Wales were from south of the projected surface track, the nearest no closer than 40 km from that line, and the furthest (Daventry, Northamptonshire) nearly 230 km distant. In Scotland, only two such reports were made, both from in or near Glasgow, about 140-150 km to the north, while in Ireland there were only three electrophonic reports at all, two in eastern Northern Ireland (at Newtownards, County Down and Newtownabbey), one in eastern Ireland at Slane, County Meath. Given the descriptions of what was heard, it seems likely most of these were genuine observations of simultaneous sounds, and in England at least, there was a mild concentration somewhat closer to the meteor's projected ground track (albeit caution is needed here, as this was also in the area of greater population densities around southern Lancashire-Greater Manchester-South and West Yorkshire).
If you saw the fireball, but haven't reported it yet, please do so as this will help fine tune the details further. You can either send an email to firstname.lastname@example.org or via the SPA Fireball report form : www.popastro.com/meteor/fireballs/reportform/index.php
The three key elements to mention in any fireball sighting are:
1) Exactly where you were (give the name of the nearest town or large village and county in Britain);
2) The date and timing of the event (remembering that British Summer Time is still in operation, so subtract one hour from current clock time to give this in Universal Time = Greenwich Mean Time); and
3) Where the fireball started and ended in the sky, as accurately as possible, or where the first and last points you could see of the trail were if you didn't see the whole flight.
If you've already submitted a sighting, many thanks! If you provided an active e-mail address, a reply will be sent in due course, but with a large number of reports in addition to the Section's usual correspondence-load, aside from further analysis of this fireball, there may be a delay. Your data is much appreciated despite that, however!
Here a selection of observer descriptions of the fireball :
David Graham (Barton, N Yorks) : The object rapidly expanded to show a visible disk with a green hue, and was several times brighter than Venus ... it passed through my zenith and appeared to be trailing a succession of fragments as it did so. It was seen disappearing over the western horizon as a cluster of glowing fragments, very much like a spent firework ... I would state that the track was Aries, Andromeda, Cygnus and Hercules
Adam Smith (Waterloo, Perthshire) : It started as a large white ball and train, fragmenting to multiple orange balls travelling to the west at a consistent altitude.
Gloria Latham (Durham) : Approached in a green bright light, as it went overhead it broke into several fragments, the main body remaining intact for a further 3 or 4 seconds, a bright jet appearing out the back, then it broke into 2 fragments which gradually decreased in brightness. A loud boom was heard about 30 seconds later
Jane Cargill (Jarrow, Tyne & Wear) : Came from north east travelling north west. Very large green oval with bright sparks in the trail. Went overhead of house - ran through to other side and outside to view, it looked like three parts by then - a middle and two side parts - loads of sparks.
Lee Scott (Blyth, Northumberland) : Heading East to West ... at first I thought it was a jet heading towards me. It looked pure bright white in the distance, then as it got closer it turned to a bright orange and appeared to be constantly jettisoning small sections of itself as it passed
Chris Reeve (Kirkcudbright, Dumfries & Galloway) : SPECTACULARLY BRIGHT! - I thought it was a low-flying aircraft at first, like a helicopter with a searchlight. As it approached, first signs of fragmentation and trail appeared around the main head. Lots of very bright colours and detail. Many break off trails all appearing to travel very straight and parallel to one another but rapidly declining and seeming to fall away as it receded
Paul White (Royton, Lancs) : The bright head of the fireball was white with a greenish hue with a long red fragment trail made up of significant number of small particles with larger fragments breaking off occasionally during its course. The tail was at least 20 – 25 % of the distance it travelled at all times until it finally burnt out.
Paul Buglass (4 miles west of York) : I noticed a very bright light low down over York (due East), to the right, and lower than Arcturus, and 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 with its landing lights pointing at us, but they were very bright, too bright for an aircraft ... 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 (very reminiscent of the Peekskill videos) as it passed through the Plough. This was the highest elevation at about 20 to 25 degrees in the Plough and appeared to be moving horizontally east to west at this point. The trajectory was very flat, so the flight path had appeared to be pretty horizontal for about 20 or 30 degrees around the Plough and East of the Plough.
It continued West in a very flat trajectory, gradually losing the bright head as it moved to the West, and slowly (very slowly) faded to about 6 or 7 glowing orange points which seemed to linger for at least 15 seconds or more until they very slowly faded from view, still appearing to be heading west, and if anything at a higher elevation than when first observed in the East ... Total observation time was possibly 60+ seconds from first sighting low in the East to fading from view in the West.
Was it a satellite re-entry ?
Early media reports did suggest that this may have been re-entering satellite debris. However, as the news item posted by Robin Scagell on the SPA web site stated, this was highly unlikely because the fireball was travelling in an approx East to West direction, whereas virtually all satellites travel in a more West to East direction (the rotation of the Earth makes it much easier to launch them in that direction).
Dutch astronomer Marco Langbroek supports this conclusion - his detailed explanation can be found at sattrackcam.blogspot.nl/2012/09/more-on-21-september-2012-fireball-why.html
Marco also speculates on a possible source for the object that produced the fireball : sattrackcam.blogspot.nl/2012/09/the-21-september-fireball-small-aten.html
Analysis of the exact fireball trajectory, including the possibility that the shallow atmospheric trajectory allowed part of it to exit the atmosphere (and unconfirmed speculation of a link to a similar fireball seen over North America 155 minutes later), is still on-going.
Fortunately, not all media reports focussed on the claims of man-made "space junk". Some focussed on witness accounts :
Others also reflected on how people unsure as to what they are seeing sometimes call the emergency services :
Added by: Tracie Heywood