NoctiLucent clouds seen from Kendal in June 2014. Image credit: Stuart Atkinson

Apr 28, 2015 Get ready for the 2015 NLC season

Sen—As I write this it's late April and spring has well and truly sprung in the northern hemisphere. Lambs are skipping about in the Cumbrian fields, blossom is heavy on the trees, and daffodils, as bright and lush as those Wordsworth saw tossing their heads in sprightly dance all those years ago, are everywhere. It's almost 9pm now, and over there, high in the west, Venus is blazing, lantern-bright, a chip of magnesium burning above and to the right of a beautiful scimitar-sharp young Moon. The two of them, shining close together in the marmalade- and plum-painted twilight, make a striking pair, and I will head out soon and dutifully take some photos of the pair. But even as the camera is clicking I will be looking longingly to the north, and wishing it was late May instead, so I could pack up my camera gear, scrunch my way up the long, steep path that leads to Kendal Castle and settle down inside its ruins to await the appearance of one of my favourite sights in the night sky—noctilucent clouds (NLC).

And I'm not alone. Already on Twitter other observers—from Scotland, northern Europe and the US—are posting impatient, finger-drumming, foot-tapping Tweets, eager to do the same. Yes, the 2015 NLC hunting season will soon begin. And I can't wait!

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NLC display seen from Kendal in July 2014. Image credit: Stuart Atkinson

Noctilucent clouds are, as my photo above, taken in June 2014, and their name both suggest, clouds that shine at night. They aren’t just "normal" daytime clouds which somehow glow at night, though. They’re clouds of ice crystals and dust that form way, way up in the atmosphere, much higher than normal clouds. So high, in fact, that, like satellites, and the International Space Station, they are illuminated by the Sun’s rays long after we have seen it set. And so, “nocti” and “lucent”. :-)

NLC are a summer phenomenon for skywatchers, regardless of hemisphere. Because the conditions which lead to their formation in the upper atmosphere only come together for a short period, essentially between the very end of May and the end of July up here in the north, as soon as Spring gets underway we start to look forward impatiently to their first appearance, and as we reach mid-July we begin to grow sad that the season will soon be over.

NLC watchers are very passionate about their beloved clouds, and, like aurora watchers, try to catch as many displays as they possibly can. Ignoring our bodies begging for sleep, we go out on any and every clear summer night in the hope of seeing something, and often end up travelling great distances to find clear skies if our own sky is blighted by cloud when word spreads across Twitter and Facebook that a big display is brewing up in the sky.

As is the case with aurora, big displays are rare. Most NLC displays are modest affairs, restricted to a few bands or patches of glowing cloud hovering almost reluctantly above the horizon. If you didn't know what they were you would easily mistake them for low cloud being lit from below by the lights of a distant factory or farm, and would pay them no attention. But sometimes... oh, sometimes the whole of the northern sky, from the horizon to the zenith is painted with NLC so bright they cast shadows, and looking at them you have to pinch yourself to prove you’re not dreaming.

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NLC display seen from Kendal in June 2014. Image credit: Stuart Atkinson

It's important to make clear here the visual differences between NLC and the aurora, to avoid confusing the two. For a start, they are different colours: the aurora paints the northern sky with a palette of red, green and purple, while an NLC display is predominantly an electric silvery-blue, with hints of turquoise, violet and lavendar. The biggest difference, however, is movement. During an auroral display the main features move, often quite rapidly, second to second. Beams of red and purple spear up into the sky, drop down again after a few moments' glory then rise again; curtains of lime green flap and slap sideways, like ships' sails cracking in the wind; arcs of colour shimmer up and down, fluttering like arcs of electricity in Frankenstein's laboratory, in beautiful silence. NLC don't do that. Their silvery-blue billows, streamers and plumes do move, but only very, very slowly in comparison—so slowly that NLC photographers have to take sequences of photographs and turn them into animated gifs to show their movement. So a good display of NLC can paint the sky for many hours, lingering from dusk to dawn, changing its appearance subtly, slowly, from minute to minute.

Trust me, a major display of NLC is something wonderful to behold, and I really want you to behold one, which is why I'm writing this article for Sen. So, how do you see these magnificent things?

The good news is you don’t need anything—no telescope, no binoculars—nothing. Because, like the aurora, an NLC display covers a large area of sky, and is bright, it is plainly visible to just the naked eye.

Having said that, a pair of binoculars is great to use on NLC, because they have a very fine, very intricate, very beautiful structure—wisps, curls, streamers and billows—that can’t really be seen well with just the naked eye. So, before the NLC season gets underway I strongly advise you (if you haven't got a pair already) to get hold of a pair of binoculars. That pair you have stuffed in a corner under the stairs, or in the garage, will do fine. And again, like the aurora, NLC are very photogenic too. You can photograph bright displays with just a hand-held digital camera, but you really need a digital SLR to take good NLC photographs. But the bottom line is this: To see and enjoy NLC all you need are your eyes, and a clear night.

Right, when can you see them? Well, the NLC “season” begins mid- to late-May in the northern hemisphere, so that’s when displays are possible, but usually it’s the start of June when the first displays occur. So, while it can't hurt to start looking from the start of the last week of May (and we will, we won't be able to help ourselves!), it's more likely that we won't see anything until the start of June.

NLC hunters will head out late in the evening on any clear summer night, to get set up at their favourite spot in plenty of time. But if you're just wanting to see a display, what time should you start looking? Well, occasionally a big display of NLC will already be in progress immediately after sunset, and looking north as twilight deepens you will be able to see something like this:

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NLC display seen from Kendal in June 2014. Image credit: Stuart Atkinson

…but that's rare. Usually nothing happens until around 11.30 pm, or even midnight, when the first traces of NLC begin to appear just above the northern horizon. At this point in a display they're not big fluffy billows or streams, they look more like sharp lines, like golden or silvery vapour trails, something like this:

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Stella Coxon from the Eddington Astronomical Society of Kendal celebrates the appearance of an NLC display seen from Kendal in June 2013. Image credit: Stuart Atkinson

Now, if you see something like that just above the horizon around midnight, it’s a good sign—it means a display of NLC might be brewing. But the keyword there is "might". It may then fade away to nothing, leaving you frustrated. That happens quite a lot, to be honest. But it's worth waiting to see what happens, because the display could grow larger and brighter, rearing up from behind that horizon like a dragon unfurling its wings. So, if you see something like this above the northern horizon late on any clear night from late May, you may be in for a treat!

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NLC display seen from Kendal in June 2014. Image credit: Stuart Atkinson

But how can you be sure if what you’re seeing is actually a display of NLC? You will be able to tell if what you are seeing are NLC because, silhouetted against the bright background sky, the “normal” clouds will look dark, like ink blotches, and the NLC, like this:

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NLC display seen from Kendal in July 2013. Image credit: Stuart Atkinson

So, having seen a hint of NLC activity low in the north, what next? Simple: you wait. Unless it’s feeling particularly evil that night, and retreats back beyond the horizon, or just breaks apart like a cobweb on a summer breeze, as the sky above and around you grows darker and darker the NLC will grow brighter and brighter, spreading upwards and outwards to cover more of the sky, shining with a beautiful mother-of-pearl luminescence that is totally unlike anything else visible in the sky.

During a major display, as the winds in the upper atmosphere catch the clouds, they form beautiful shapes—ghostly streamers, curls and tendrils of silvery-blue light, like some kind of “phantom” or “energy field” special effect from a science fiction film. Many NLC show a distinctive cross-hatch pattern, and through binoculars you will be able to watch the insides and edges of the clouds changing shape almost by the minute, sculpted by the silent winds blowing high, high above the Earth. If you’re really lucky you’ll witness an NLC "storm" that covers half the sky or more, and then trust me, you’ll just stand there, shaking your head in disbelief, as the heavens are painted a dozen different shifting shades of electric blue and silver by Nature.

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NLC display seen from Kendal in June 2014. Image credit: Stuart Atkinson

If you are lucky enough to see an NLC storm, and have a camera, you absolutely must try taking some photographs. If you're not an experienced astrophotographer who knows about taking time exposures etc, don’t worry about twiddling settings and dials too much. Just set your camera on Auto and click away, you’re bound to get something. But if you can control aperture and exposure, try taking some long exposures of several seconds to ensure you record the NLC in all their glory. You’ll need to have your camera on a tripod, make sure your focus is pin-sharp (set your lens to manual, not AF, and focus on a bright star before taking ang NLC photos) and be using a standard 50mm lens or a wide angle lens to take your photographs. If the display is bright, set your camera to 400 ISO and do exposures of just a couple of seconds. If it’s a faint display, try longer exposures. If it’s a particularly vivid display, with a lot of detail and structure, put your best zoom lens on your camera and try some close-ups of individual whirls, curls and whorls. Basically, just have fun with it, but make sure you don't watch the whole display through your camera—step away from it often and just drink in the view.

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NLC display seen from Kendal in June 2014. Image credit: Stuart Atkinson

So, now you have all the information you need to start hunting NLC as the 2015 season approaches. I really hope you get to see a display before too long. Last year's season was fantastic, with several major storms and lots of decent displays too, so fingers crossed 2015 is as good as 2014 and hopefully better.

Another important thing to think about is how you're going to know when to go out and look for NLC. Although dedicated NLC hunters will go out on any and every clear night through the summer, in the hope of seeing something, not everyone has the time to go and do that. Everyone has a busy life, and I know many of you reading this just won't be able to head outside for a few hours around midnight just in case something happens. You'll want to know you're going to see something, right? So, how can you improve your chances of seeing the next big NLC display—or, even better, how can you guarantee not missing one that is underway? This is where the internet comes in.

Back in Ye Olde Days, before we all lived on computers, smartphones and tablets connected to SKYNET, amateur astronomers who wanted to see displays of the aurora or NLC had to physically go outside and check the sky every clear night, often waiting hours just in case something happened. Or, if we were lucky, we belonged to an astronomy society, or had a network of fellow aurora or NLC fans, who would ring around, alerting its members to a display. But now, in this Apple and Android Age, we have online observing groups and communities who post alerts and real-time observing reports on Twitter and Facebook.

Now, I know not everyone reading will be on, or will want to join, either of those social media time sponges, and I know neither is perfect, but really, both are fantastically useful resources for amateur astronomers, great for spreading information, advice and help. If you’re already an active Tweeter, all you have to do is start following one of the NLC groups on there. Just enter #NLC into the search window and you’ll find one to Follow. If you’re not on Twitter, then I strongly recommend you join, because if you don’t then there’s a very good chance you could miss the next great NLC display, and then you’d be kicking yourself when you read about it and see the amazing photos taken by others the next morning, wouldn’t you?

And Facebook? Just as useful, with lots of NLC-watching groups just waiting for you to join them and hunt NLC with.

Finally, a word on the most important thing you need to be an NLC watcher: patience! You'll need lots of it whilst looking north and scanning the sky, waiting for a display to start. Just like meteor- and aurora-watching, it's so easy to get fed up after nothing has happened for a long time, and when you're feeling cold and tired, and that silky voice starts whispering "Go home... go home... nothing is going to happen..." in your ear you'll have to be strong enough to ignore it. And you'll need patience during a display too, because an NLC display can fool you: you can watch a display that seems to fade away, and die, and convince yourself “That’s it, it’s over”, only for the NLC to suddenly brighten again and develop even more complicated, even more intricate structure and detail. Give in and pack up too early and you risk missing something spectacular. This happened to me last year. A modest display appeared one night then died away to almost nothing after an hour, at around 1am. I was absolutely shattered, and with an early start at work that morning I was this close to going home, but I stayed, and at 2am the display returned with a vengeance, and within half an hour was one of the best I have ever seen in my life, as the photo below shows.

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NLC display seen from Kendal in June 2014. Image credit: Stuart Atkinson

It really comes down to one golden rule: once you’re out, stay out, until you’re absolutely sure that the show is over. Then stay out just a bit longer. You know, just in case...

That’s it, that's your guide to the 2015 NLC season. I know I haven’t really gone very deeply into the science behind NLC here, and I'm not going to because a) I'm primarily an enthusiastic observer, and b) there are lots of really detailed and in-depth NLC websites which can be found with a simple Google search, and they all explain the science very well. A good place to start tho, is Martin Mckenna’s excellent site, here.

I hope you’ve found this introduction to NLC useful. For our southern hemisphere readers, this information will be useful to you in 6 months, when you are approaching your summer, but I hope that when the time comes you'll look back at it and find it useful then.

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