Bovedy meteorite

In a previous post I mentioned my search for information about a meteorite I actually saw fall while at Reading University. It's surprising that I found it so hard as it turns out to be quite notable. It's even mentioned in one of my astronomy books that I've had for years!

It's known as the Bovedy meteorite, after the place in Northern Ireland where the largest fragment was recovered, and fell on 25th April 1969 at around 21:25. A second fragment fell through a roof in Sprucefield. I'm obviously interested because I saw the meteor, and wanted to remind myself about it. (Note: a meteor is what you see in the sky, it's a meteorite when it hits the ground.)

I looked up the Times archive for the following day (now I know where to look!) and found a pretty lightweight item titled "The night a star fell on Ireland" that was a report from the Ballymurphy and Ballynahinch area of Co. Down. The internet however has far more useful data.

The most confusing thing for me is the track of the meteorite, because it doesn't agree with what I remember.

An article in Nature (3) includes a map showing the estimated track based on an extrapolation from the location of the retrieved fragments. This shows the meteorite crossing the English south coast at around Bournemouth and travelling in a NW by N direction. That this track is based on two hard facts about the meteorite, namely the location of where pieces fell, makes it pretty convincing. However, I'm unhappy with it because it conflicts with my memory of the incident. Memories can certainly be untrustworthy after 45 years, as shown by the fact that I remembered it happening in the summer (that was because it was in the evening and still light, or at least not dark, so I think I can be forgiven), but I do clearly remember where I was and what I was doing.

I was in St Patrick's Hall of residence at Reading University, playing bridge, and sitting facing the window. My room was in "K" block, where the windows face directly north-west, and my clear memory is seeing the object in the sky tracking to the left, and we watched it until it disappeared over the horizon. From this observation, the meteorite must have passed to the east of Reading, whereas the Nature track puts it 50 miles to the west, and so it would have appeared to track from left to right. I'm not sure I would have even seen it if this was the case.

Red track from Nature, blue track corresponds more with my observation

In the map, the numbered points are:
1 - Bovedy
2 - Sprucefield
3 - Shrewsbury
4 - Salisbury area
5 - Reading
6 - Preston
7 - Doncaster
8 - London
9 - Sussex area

So could the Nature track be inaccurate? It does look pretty convincing, but I can't shake the fact that it's not consistent with what I remember. The big problem with a track that is consistent with my memory is of course that it doesn't pass through the two fragment sites. This isn't necessarily impossible - fragments fall a long way and can be surprising affected by wind, although I have no knowledge of the wind conditions on that night.

Looking at other information, the The Meteoritical Society record (1) says "The fireball was seen all the way from Sussex through London, Doncaster and Yorkshire to Northern Ireland toward Belfast." - all the points in England well to the east of the Nature track. Another report (7) mentions an observer in Preston, Lancs, and another who saw it "over Shrewsbury". Also, it says "It was moving from ESE to WNW very rapidly." (like my track). The Nature track puts it travelling NW by W, a less oblique angle. These all suggest a more easterly track.

To be fair, the observations apart from mine aren't necessarily a problem: given the height and brightness of the meteor it would have been visible from a long way away. Also the greatest population of the UK lies to the east of the country, so sheer numbers would suggest that is where most observations would be made.

Perhaps I just have to accept that my memory is wrong. It may not have been as impressive as the Chelyablinsk monster but it was impressive nevertheless, and probably the biggest I will ever see.


There's also the question of how big the original object was, and how much of it was recovered. In The Data Book of Astronomy, Patrick Moore said "The Bovedy meteorite was well observed during its descent, but the main mass was not recovered, and almost certainly fell into the sea". Everything I've read only mentions the pieces found as "fragments" - I don't think anyone suggested that the object found at Bovedy was the main body of the meteorite. I vaguely remember from the time that some wild figures were kicked about (100 tones? 1000 tons?). More reasonably, the rounded shape of the Bovedy fragment suggests to me that is was part of a roughly football sized object, which would be around 20 kg given the normal density of stony chondrites.

In general - and it's so dependent on factors like size, speed and angle of descent - meteorites become visible at a height of around 100 km, and, assuming they've not burned up entirely, have slowed enough to stop ablating and become invisible at around 20 km and at a speed of 2-4 km/s, thereafter taking up to 3-4 minutes in free-fall to reach the ground (8,9).

Using these assumptions, it's possible to estimate roughly how far the main body of the meteorite may have travelled. It was still visible at Bovedy as it reportedly passed overhead (2), so if we assume it was 100 km high when first seen over southern England, and 20 km high at Bovedy, a distance covered of approx. 500 km, then this gives an angle of descent of about 10 deg.

Using all this, projectile dynamics (and taking into account air resistance) gives the following distances to the ground and time taken for a 20 kg spherical object, for various initial dark flight speeds:

Speed(m/s) Distance(km) Time(secs)
 2000         31         101
 3000         35         100
 4000         39          98

This would support Patrick Moore's assertion that it ended up in the sea.

In truth, I accept that it's probably nonsense to attempt calculations like these. Too many assumptions based on inaccurate data and guesswork. But I enjoyed doing the calculations!

References

1. The Meteoritical Society Bulletin Database record (http://www.lpi.usra.edu/meteor/metbull.php?code=5121)

2. The UK and Ireland Meteorite page (http://www.meteoritehistory.info/UKIRELAND/NEIRE.HTM)

3. Recent Fall of the Bovedy Meteorite, Northern Ireland, Nature, vol 23, July 25 1969 (images)

4. The Data Book of Astronomy, Patrick Moore, p248

5. 40 years since the sky fell on Ulster (http://www.newsletter.co.uk/news/regional/40-years-since-the-sky-fell-on-ulster-1-1884295)

6. The night a star fell on Ireland, (London) Times newspaper article, April 26 1969

7. Turning UFOs into IFOs; Part 1: Fireball Meteors (https://planetpreternatural.wordpress.com/tag/bovedy/)

8. Fireballs and Meteorite Falls, International Meteor Society (http://www.imo.net/fireball/meteorites)

9. American Meteor Society, (http://www.amsmeteors.org/fireballs/faqf/):
"At some point, usually between 15 to 20 km (9-12 miles or 48,000-63,000 feet) altitude, the meteoroid remnants will decelerate to the point that the ablation process stops, and visible light is no longer generated. This occurs at a speed of about 2-4 km/sec (4500-9000 mph)."

 

Update Feb 2024

I heard from Paul Littler who recently contacted me after reading this. He also saw the meteor that night from where he lived not far from Merseyside, and as with me it made a lasting impression on him. Paul had done more research than I'd done, and had contacted the Armagh Observatory where most of the recovered pieces are now kept. They told him that the meteor would have been the size of an American Fridge when it entered the atmosphere. A quick calculation using the average meteorite density of 3 gm/cc yields a size of around 3 metric tons!

This seems enormous, and you'd think one of the largest seen to fall on the UK. But meteors are recorded by the size of recovered meteorite fragments, without much or any speculation of initial size, and in terms of recovered weight (3 fragments with a total weight of around 8 kg), the Bovedy meteor ranks only 11th on the UK list. Nevertheless, since some or most of it probably landed in the sea, it may well still be one of the largest observed falls.