This text is taken from BAA e-bulletin 698 written by John Mason.
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 email@example.com or to firstname.lastname@example.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
The Geminid meteor shower is now underway, with peak activity expected during Wednesday, 14th December. Unfortunately, weather forecasts indicate very variable observing conditions across the British Isles and Northern Europe, so it is important to have a good geographical spread of observers to ensure adequate coverage. The waning gibbous Moon will also be rather obtrusive, so observers are advised to direct their gaze away from the Moon, or to hide the Moon behind an obstruction such as the wall of a house.
The Geminids are currently the most active of the regular annual showers, with rates outstripping those of the Perseids for a 24-hour interval centred on their 14-15 December maximum – a real treat for observers prepared to brave the cold, damp and windy weather.
This year, Geminid activity is expected to peak at about 14h on Wednesday, December 14th, when the peak Geminid Zenithal Hourly Rate may reach 140 m/h – sadly during daylight hours for observers across Europe. The maximum is broad, however, and it is important to have a spread of observers making observations throughout the nights of 13th/14th December and on 14th/15th December to ensure adequate coverage of the shower maximum. In addition, observations by BAA members in North America and the Far East will be welcomed by the Meteor Section to improve coverage of the period of peak shower activity.
The Geminid radiant (at RA 07h 32m Dec +33o, just north of Castor) rises early on and reaches a respectable altitude well before midnight, so observers who are unable to stay up late can still contribute very useful watches. On the evening of Wednesday 14th December there is the added bonus of an increased proportional abundance of bright events after maximum; past observations show that bright Geminids become more numerous some hours after the rates have peaked, a consequence of particle-sorting in the meteor stream.
Geminid meteors enter the atmosphere at a relatively slow 35 km/sec, and thanks to their robust (presumably rocky/asteroidal as opposed to dusty/cometary) nature tend to last longer than most in luminous flight. Unlike swift Perseid or Orionid meteors, which last only a couple of tenths of a second, Geminids may be visible for a second or longer, sometimes appearing to fragment into a train of ‘blobs’. Their relatively low speed and the abundance of bright events makes the Geminids a prime target for imaging.
For further information, or copies of report forms, observing notes, and details of how to carry out group meteor watches, please visit the BAA Meteor Section website at http://britastro.org/meteor
There is the possibility of an unusual outburst of Draconid meteors on the evening of Saturday, 8 October 2011. The meteors are connected with periodic comet 21P/Giacobini-Zinner, so the shower is also known as the Giacobinids.
The Earth intersects a number of dust trails laid down by the parent comet during the evening of 8 October.
The first and most probably weaker outburst, due to a number of rather old trails, is likely to occur sometime after 16h UT, but the timing is uncertain and will favour observers in Eastern Europe and the Middle East.
A second and more likely stronger outburst is possible sometime between 19h and 21h UT but the outburst, if it occurs, is likely to be sharp and brief.
Observations across all longitudes are important, but it will be essential for would-be observers to be far enough north to ensure that the radiant is at a respectable altitude above the horizon at that time.
The peak rates of these outbursts are highly uncertain, and no meteor storm is likely. Estimated peak levels of meteor activity range from 40 meteors per hour to 800 meteors per hour. The only way to find out what happens is to go out and look for yourself!
Unfortunately, there will be a waxing gibbous Moon in Aquarius, less than four days from full at the time of peak Draconid activity, so there will some interference from moonlight. Observers should look to the northern half of the sky, keeping the Moon behind them.
The radiant of the shower will be near the star Nu Draconis in the ‘head’of Draco. Draconid meteors are typically very slow moving, in marked contrast to members of showers such as the Perseids or Leonids.
From the British Isles, observers should go out as soon as twilight falls on the evening of Saturday, 8 October.
Observations will also be of considerable value on the evenings immediately before and after the predicted peak to provide a check on background meteor rates at this time. Let’s hope for clear skies everywhere on the evenings of 7, 8 and 9 October 2011, but particularly on the 8th!
The BAA Meteor Section would welcome any observations of the Draconid meteor shower this year from individuals or local society groups, using any of the observing methods outlined on the BAA website. Visit our Draconid Meteor Project page’. Even simple counts of meteors seen within given time periods will be welcome.
It is intended that a summary of all the observations received, crediting all of the individual observers and society groups, will be published in the BAA Journal as soon as possible after the event.
Always the summer’s main attraction for meteor observers, this August’s display of the Perseid meteors should be particularly favourable given that the peak occurs just a couple of days after New Moon and, consequently, there will be absolutely no interference from moonlight. We hope that observers will make every effort to cover the shower well this year, and send in their observations to the BAA Meteor Section.
When to Observe
Perseid activity may be evident as early as the third week of July, although there will be considerable interference from moonlight at the end of July since the Moon is Full on July 26. Activity takes a marked ‘kick’ around August 7/8, but by this time the Moon will be virtually New and watches may be carried out from this date right through until August 15/16 under dark, moonless skies. We hope that, weather permitting, observers will cover shower activity throughout this period, including nights away from the main peak.
The Perseids are expected to peak around 22h UT on August 12, making the hours from dusk on August 12 to dawn on August 13 probably the most productive for observers in the UK this year. Good observed rates may be expected in the early morning hours on August 11/12 and 12/13 as the shower radiant (RA 03h 04m Dec +58) climbs high into the eastern sky. Perseid shower activity will be starting to decline by the time darkness falls on August 13.
All else being equal, the best observed rates are found when the Perseid radiant – near the ‘Sword Handle’ star cluster on the Perseus-Cassiopeia border at maximum– is highest in the sky during the pre-dawn hours. However, even in the early evening, the radiant is already at quite a favourable altitude as the table below shows:
|Local Time (53°N)||Radiant Altitude||Local Time||Radiant Altitude|
Observers should bear in mind the nightly eastwards ‘drift’ of the Perseid radiant due to Earth’s orbital motion. In early August, the radiant is 15 degrees west of its position at maximum (given above), to the north of Andromeda.
The Parent Comet
The Perseids are associated with Comet 109P/Swift-Tuttle, which was last at perihelion in 1992. Enhanced activity accompanied that return, and was evident for several years, up to at least 1997. The 2005 and 2007 returns of the shower proved fairly ‘normal’, with a single sharp peak to ZHR ca. 80 in 2005 (perhaps slightly lower – ca. 70 – in 2007), and the usual slow rise to and steep decline from maximum. In 2008, there was a notable sharp spike in activity rising to in excess of 100 m/h after the ‘normal’ maximum. As always, the 2010 return of the shower requires careful scrutiny on all possible clear nights (and not just at maximum!). The normal limits of the shower are from July 23 until August 20.
The Perseids are well known for the abundance of fast, bright meteors close to their maximum. Perseid meteoroids enter the atmosphere at a velocity of 60 km/sec, and the resulting meteors often leave behind persistent ionisation trains. The large numbers of bright events in the five-day interval centred on Perseid maximum makes this an excellent target for photography, considering the absence of interference from moonlight this year. Conventional film now remains the medium of choice for relatively few observers, with most having made the transition to digital SLR cameras.
With a static (undriven) digital camera, mounted on a sturdy tripod, and operated by a pre-programmed digital timer control unit, exposures should be kept short – about 30 seconds duration – with the speed set to ISO 1600 and a wide-angle lens set to maximum aperture. Remember that a super wide-angle 20mm focal length lens on a Canon DSLR, for example, has the coverage of only a 32mm lens on a full frame 35mm camera and 18mm becomes the equivalent of a 29mm lens on 35mm full frame. Such a set up, under good sky conditions, can capture meteors of magnitude 0 and brighter. Ideal aiming directions are about 20-30 degrees to one side of the radiant at 50 degrees altitude above the horizon – Cygnus in the early evening, the Square of Pegasus later in the night, or towards the north celestial pole, for best results.
Reporting of Observations
For further information, or copies of report forms, observing notes, and details of how to carry out group meteor watches, please visit the BAA Meteor Section website at http://britastro.org/meteor or contact the Acting Director of the BAA Meteor Section.
A new simplified explanation of how to fill in the visual meteor report form and an electronic version of the form may be found at:
Please submit your observations to the BAA Meteor Section as soon as possible after you have made them, and at any rate within one month at the most. Observations should be sent to the Acting Director, who will be pleased to answer any queries regarding further aspects of meteor work:-
Dr John Mason, 51 Orchard Way, Barnham, West Sussex PO22 0HX.
Email docjohn [at] dircon [dot] co [dot] uk