On the evening of the 4th March Peta and I drove up to the observatory to man the domes for Graham Bryant’s weekly Astronomy course. It had been a shocking day with heavy rain and hail for most of it. After getting soaked walking from the car park to the clubhouse, it wasn’t altogether surprising when Graham agreed to call off observing for the night. So we drove home. As we parked up we saw the top of Orion and started to wonder if we had made that call just a tad too soon. But it was done and there were still heavy clouds from the southern horizon up to Rigel, so we settled down for a quiet evening. Getting up early the next morning I was surprised to see just how crisp and clear it was. Oops !
And so I thought nothing more about it until a couple of days later when I decided to catch up with my meteor camera checks. Nothing amazing until I saw this on the South East camera …
A storm I had been completely oblivious to at 00:46:22 ! And what was were those odd spikes ? Nothing for it but I needed to download the files to take a look - which is when I always start to curse BT for the speed of the line they provide to the observatory! The good news was it was a ‘normal’ sized file so it would only take around ten minutes - and that size already hinted at what I would find. Finally downloaded, I was able to confirm they were sprites and with the aid of IrfanView, I isolated the single frame (frame 31) …
Continuing to check the rest of the clips for that night, I found a further 3 at 00:55:53, 01:02:25, and 04:05:28. Interestingly, had I only captured that last one, then I would have probably written it off as a fairly run of the mill cosmic ray, and deleted the clip.
It was the tricorn-like forks in the others, especially the first two, that gave them away for what they were. So I posted an image on Facebook of the best one (the second) and waited to see if anyone else had caught them …
A few “wows” later, and after posting them to FiRes (at Richard K’s suggestion), I had a couple of positive responses from Ash Vale (Richard K himself), and Wilcot (Richard F).
So, what to do ? I had processed mine through UFO Analyser but, as expected, I got three _flash’s and a _none ! Even so, Analyser gave me direction arrows on the Ground Map to the flashes it had detected (or the corner of the frame in the case of the _none). In reality, only one of those flashes was from a sprite - the other two were somewhere else in the frame, but that got me thinking and I turned on the profile (selected the current profile on the Plot Tab) which is really a plot of the frame stretched out to 80/100/120 kms high - way above any storm.
I could see (or work out roughly) the direction to the sprite using a ruler on my 27 inch monitor, and a calculator to determine the offset where the flash didn’t coincide with the sprites. So now I needed to triangulate with one of the other observations and I asked Richard K for copies of his profiles so that I could Analyse his clips. I got hold of the clips (many thanks Richard) but, for what reason I do not know, I could not get them to process successfully. Darn !
However, I realised that if I displayed his profiles, I could repeat the manual plotting that I had done for my own clips using the position of his sprites within the captured frames.
Several rulers and calculations later I had matches which I then plotted (in yellow) onto the Ground Map in Photoshop. I still had two events that did not match with Richard’s so I had to make an assumption, which was that the storm was contained (ie not everywhere) and travelling in an orderly fashion west to east up the Channel, as suggestion by the three full triangulations.
So I plotted the two remaining sprites (in amber) on the ground map “roughly” where my directional arrow crossed the path of the storm, giving a final plot of the night’s sprite encounter, as follows …
Let’s be clear, if these were meteor events, the accuracy would be hopelessly inadequate, but for a storm which was clearly out at sea, placing the events within a couple of miles seems to me to be sufficient. I did contact someone in northern France to see if he had caught them from “the other side”, but unfortunately he was clouded out.
One final observation: whilst all the sprites captured appeared on frame 31 of their respective videos, for a couple there was a ‘shadow’ image on the following frame - I’m not sure whether this is due to the interleaving process, or just the timing of the event, or something else - my jury is out on that.
So there you have it. In an otherwise quiet period for meteors, we can still get some interesting science out of our network of cameras. I’m not sure how to explain the form of the sprites we captured, especially the short straight ones which accompanied the usual upward pointing forks - perhaps an atmospheric scientist would like to comment ?
Vice Chairman of Hampshire Astronomical Group
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