|
|
 |
 |
 |
 |
 |
 |
 |
 |
On April 8th 2010 a B-class solar flare erupted from the Sun unfurling a full halo coronal mass ejection (CME) which was heading directly for Earth, impact time was estimated for April 11/12th when observers at northern and mid northern latitudes had a risk of seeing a geomagnetic storm. During daytime on the 11th the impact from the CME was already disturbing the magnetic field causing red alerts over high lats and yellow alerts over mid lats, unfortunately this was happening during daylight so nothing could be seen, on the positive side the activity was expected to continue on and off for the next 12 hours so we eagerly awaited for darkness to fall. After sunset Conor McDonald and I had been monitoring the online aurora charts and we had already decided that a watch would be undertaken once active signs presented themselves. For a while things remained calm until early night time when the charts suddenly came to life, often when reading these charts it's advisable not to sit in front of the computer waiting to get very strong values before doing a watch, this often leads to disappointment with the inevitable result that the aurora has already happened, especially if it was a brief event. For this reason it's much more productive to think ahead and note the tell tale signs which could indicate an aurora event in the near future. This is exactly what happened, we noted the IMF tilting south with increased dynamic pressure and solar wind speed, this told us that there was already good potential, the south-tilting IMF was the most important factor of all. We didn't bother waiting on the auroral oval to grow or KP index to rise because these would always follow suite later, and can often be delayed, so should not be relied upon for real time forecasting.
Conor and I have been observing auroras for many years and have spent more than enough time studying the moods of the charts to know when to get away from the computer and get out under the stars. In truth, the only way to increase your chances of seeing an aurora is to complete a visual watch, this has produced great success in the past so we stayed faithful with our method and decided to hit the road. By great fortune we had been getting a series of wonderful clear nights due to high pressure affecting all of Ireland so we had everything going for us. This was not our first aurora watch of the season, over the previous week Conor and I had done many watches covering all the low-risk geomagnetic forecasts, these where long cold nights spent in rural areas, other nights produced nothing but cloud. We both had a good feeling about this CME event and already felt confident we would catch something over N. Ireland.
Originally we where going to observe from the North Coast over-looking the Atlantic Ocean which would have been fantastic, however with things kicking off quite quick on the charts we decided the journey would be too long and a waste of fuel if we ended up missing something while on the road. On a whim he decided on a local spot, we needed somewhere elevated, with a good horizon, and dark. The answer was just up the road from us, the old faithful Glenshane Pass. We arrived at our chosen spot on a narrow road and just parked the car at the side, once we stepped outside into the cold air we knew we had made a good decision. Once we acquired full dark adaption we were impressed with the quality of the sky, the stars were brilliant against a dark background and Mars beside the Beehive seemed to jump out from the sky. It was completely calm, dry, and silent, except for the yelp from a Fox somewhere over the hills. The northern horizon was quite decent although there was some light strips of cloud and low mist which wasn't threatening at all.
At approx 00.30 BST we saw an aurora, it was a simple as that, we both looked to the N at the same time and spotted it immediately, there was no question about it, there was an aurora present along the N to NW sky sector, the quiet night was broken by excited chat and visual remarks comparing what he saw. We both agreed it was 13 degrees (26 Moon diameters) above the true horizon and most certainly the real deal. To begin with it was just an enhancement to the sky which shouldn't have been there, the kind of glow which others might have mistaken for light pollution glow, however its form and shape gave itself away. As the min's ticked by it seemed to get better and better and soon it was quite bright to the naked eye.
 |
00.43 BST, 98 sec's ISO1600 at F/4.5
I set-up the camera and began to take exposures, the first images had picked it up with ease and it seemed to be getting much brighter. This was our viewing location looking NW (L) to N (R) from Glenshane, the narrow road can be seen below leading into the distance towards the aurora. By this time we were on a high enjoying the aurora which was the best we had seen since the 2005 Halloween geostorm. We both stood in the frame for this shot with our arms in the air in celebration. For those who don't know, the green, red, purple, and blue colours are part of the aurora, the orange glow is light pollution reflecting off the mist from distant towns. With the naked eye the LP doesn't look like that at all, to us the sky was almost completely black, long exposures on cameras tend to exaggerate the effect of LP. All of these images were taken with the Canon 450D using the 18mm kit lens with a remote shutter. In the sky can be seen Auriga, Perseus, and Cassiopea.
 |
01.04 BST, 106 sec's ISO1600 at F/4.5
By this stage the green band had really intensified and could be seen stretching for more than 60 degrees in length. Note the 3-4 purple vertical rays above the road between Algol and Almach. Visually, we could see enhancements within the band which waxed and waned. We had already been observing it more than half an hour at this stage and the conditions were dramatically improving as the high level cloud began to move away and the sky became much more transparent down to the local horizon which really helped out the exposures.
 |
01.52 BST, 66 sec's ISO1600 at F/4.5
The aurora looked great at this stage, I had been taking exposure after exposure and found out that the best results were obtained with a shutter speed between 60 and 70 sec's, anything more than that made the ambient sky glow too bright which resulted in less contrast and detail so I stuck to what worked best. By this stage we were so familiar with the aurora that we watched it while chatting away like normal, the only difference being that we talked with greater animation due to the thrill of being out here under the Northern Lights. Conor went back into the car and switched on the heater to warm up, his rear lights illuminated the fence posts during the exposure. I was very happy with the images I was getting and I was glad I had taken extra time to get the camera focused at the beginning of the session using Vega which showed up very clearly on the live view.
More exposures, then more, when I previewed the next batch I was horrified to see a bright purple glow on the images to the lower left hand side, it took me a while to figure out why this was so, I was using live view the entire time and had forgotten to switch it off so the camera heated up with repeated use which caused that strange artifact on the image. I disabled live view then switched the camera off for a while hoping that this was the reason. After 5 min's I tried another exposure and the image was perfect with no purple glow, thank goodness for that, so I went back into action.
 |
02.04 BST, 57 sec's ISO1600 at F/4.5
The aurora was at its absolute finest around 02.00. What amazed us most was how the aurora just vanished before our very eyes, at first I thought it was my eyes playing tricks so I said nothing, then Conor said ''is that fading away'' which confirmed it. It wasn't like a gradual or rapid fade, it was more like a green veil was being pulled down towards the horizon by an invisible hand, the motion was similar to the retreating tide on a beach before a Tsunami. The aurora was gone completely with barely a trace remaining in the sky then suddenly it came back again with vengeance.
The green band became intense and proud with excellent definition then vertical rays/beams began to shoot skyward, at first they were faint and appeared in the NW within Auriga, with another in Perseus, so I panned the camera in that direction to get a capture. While the camera did it's thing a new set appeared to the N and W of N which completely blew the others away. One of those rays was truly spectacular, it extended over 20 degrees high towards Cassiopeia and began to brighten further as it slimmed in form like a pencil line. Conor was shouting and pointing saying ''look look'', ''get an image quick!'', I was hoping the ray would stay visible for long enough, and it did. I had just enough time to turn the camera around on the slightly sloping road, level the tripod, then take the shot. This turned out to be my best image of the night, that bright ray can be seen along with a fainter one to its left.
 |
02.08 BST, 64 sec's ISO1600 at F/4.5
Same region after the main ray faded, there are at least three regions with faint vertical rays between the trees and telegraph pole, some with subtle purple colours. The L beam points straight up to the Double Cluster, with the middle beam between Cassiopeia and Lacerta. The white-blue light on the ground behind those trees belongs to distant cars and trucks traveling along the main Glenshane Pass road, even at this hour of the night there's regular traffic on that busy road.
 |
02.16 BST, 60 sec's ISO1600 at F/4.5
Camera panned more NW where I spotted two more vertical rays. The red colour is part of the aurora, you can see the cut off point where it ends and darker sky begins, that point was somewhere above Capella. If you compare this image with the first one you can see how much the stars have changed with time. Note how Algol was once above the green band, however here it's almost within it. I had so many images taken that when I previewed them on the screen, and flicked through them, I could see a time lapse of the aurora showing the beams moving across the sky which was very cool.
 |
02.18 BST, 80 sec's ISO1600 at F/4.5
I had just realised that this was the 80th aurora display I have observed since I first got into the night sky many years ago, it was thrilling to see yet another and celebrate in style. I had a strong feeling 2010 was going to be a great year for mid latitude aurora displays, and so far that has been the case, and I very much feel bigger displays will be on the way soon. The Sun has woken from its record solar minimum slumber and is now beginning to show off with regular new sunspots and CME eruptions, and with solar maximum only 3 or so years away things are going to get very interesting indeed so expect many more aurora images on here in the future.
Conor and I called it a night at 02.30, as we drove down the road we could see the aurora through the window above the dark Sperrin Mountains. Once back in Maghera I could see it until 03.30 making this display a 3 hour event, it still managed to throw up several more huge rays through Perseus and Auriga however the sky was very murky at ground level so I didn't take any more images. It had a been a great success, all those previous nights of watching had finally paid off and it was that wait which made the result all the more satisfying. I checked the computer when I got home, the KP was at 6 (storm) and a G2 Geomagnetic storm was in progress with observers in Europe reporting sightings.
Martin McKenna