I have been watching an oak tree for over two hours. It’s gone midnight, and it’s now so dark that the tree is no more than a hazy silhouette. I’m meant to be recording bat activity in and around the tree, but by this point in the morning the whole thing seems pretty futile. The bat detector I’m holding might register their ultrasonic calls, but I can’t see if the bats are flying into the tree, out of it or just flitting overhead. All I can do is write down the time of each bat’s call, the species (predominately Common pipistrelles) and in the activity column on my sheet ‘Bat not seen’.
At half past midnight I pack up my kit and make my way over to the other ecologists. There are five of us on this survey, and each of us has been monitoring a particular tree. We’re keen to get to bed, as in a few hours time we’ll be back out watching the trees again. This type of bat survey is called a ‘dusk-dawn’ and, as the name suggests, they start at dusk and end at dawn, with a precious few hours for sleep during the interim. Early in the survey season, around April, and at the end in October, dusk-dawns aren’t so bad, as you can get a good few hours sleep in-between. But in the middle of summer, on the summer solstice, as this survey is, the days are so long that there is barely any time for sleep. In fact for weeks before and after the summer solstice the UK never enters true ‘night’, lingering instead in astronomical twilight, which is dark, but not the saturating darkness of winter.
We pile into a car and start driving towards the nearest Premier Inn. I’m in the back on the passenger side, staring out of the window in a sleepy stupor. As we reach the dual carriageway I see a glowing patch in the sky; long fibrous strands of cloud stretched out like silver hair, hanging above the remnants of dusk.
“Guys, look!” I say. “Those are the clouds, the glowing night clouds.”
I’m met with strange looks from four very tired people. Even so, I find it hard to curb my excitement. I’ve been hoping to see these clouds for years. Had I been on my own I would have pulled over, climbed out of the car and stood by the side of the road in awe. But with four sleepy colleagues surrounding me, I dare not ask if we can stop. Instead, I silently stare at the glowing clouds until we reach the local town and the clouds are obliterated by street lights and billboards.
The glowing clouds I saw that morning were noctilucent clouds, which means ‘night shining’ clouds, otherwise know as NLCs. They are high altitude clouds, forming in a layer of the Earth’s atmosphere called the mesosphere, fifty miles high. They were recorded in 1885 by Otto Jesse, two years after the eruption of Krakatoa, one of the deadliest volcanic events in recorded history. Jesse had been observing the unusual sunsets created by the eruption when he noticed the NLCs. He organised photographic observations of the clouds (originally thought to be made of volcanic ash, which was disproved by Malzev in 1926) with Foerster and Stole and, after the first year, this work was continued by the Berlin Observatory until 1896.
Noctilucent clouds are strange things, especially when we consider that before 1885 there is no record of them. Given that there was so little light pollution back then, this seems curious. Surely, had noctilucent clouds been around before 19th century, they would have been seen by someone?
Not necessarily. Noctilucent clouds form because of tiny dust particles in the upper atmosphere, dust which is thought to originate from meteors and meteorites, (about 44 tonnes of meteoritic material falls on Earth each day) volcanoes and man-made pollutants. Water vapour rises high into our atmosphere and attaches to these dust particles where it forms tiny, reflective ice crystals; the make up of NLCs. Due to rising levels of methane in our atmosphere, there is more water vapour in the mesosphere now than there was 200 years ago. Although there are natural sources of methane, historical graphs show an unprecedented rise in levels in the Earth’s atmosphere after the Agricultural and Industrial Revolutions. This is because fossil fuel operations, waste and agriculture emit millions of tonnes of methane into the atmosphere every year. (Take a deep breath if you want to look at our current methane levels, which are around 1925 PPB. That’s an increase, in just a few hundred years, of about 65%.) Methane is a powerful greenhouse gas. It might have a shorter life span in the Earth’s atmosphere than carbon dioxide, but it is 25 times better at trapping heat, which is very bad news for our climate.
The increase in methane, and therefore moisture in our upper atmosphere, explains the arrival of the hitherto unrecorded noctilucent clouds. Water vapour is thought to decrease the temperature in the mesosphere, enabling more ice crystals to form, so the more methane we emit, the higher our chances of seeing noctilucent clouds (although researchers have noted that there is a relationship between NLCs, ultraviolet radiation and the solar cycle, which must also be taken into account. Due to the temperature fluctuations it causes in our upper atmosphere, when the Sun is more active, fewer ice crystals form, decreasing our chances of us seeing NLCs.) It seems not all clouds have a silver lining. Noctilucent clouds might appear silver sometimes (and blue, red and green) but their appearance is linked to a potent greenhouse gas.
After my first sighting, I kept a look out for noctilucent clouds for the next few summers, but sadly had no luck. Then, on the 27th March 2020, comet NEOWISE was discovered (officially known as C/2020 F3). It made its closest approach to Earth during July of that year, growing to a magnitude of 0.5 – making it the brightest northern-hemisphere comet since 1997’s Hale-Bopp, which I remember watching from our back garden as a child. At its brightest, NEOWISE was easily visible to the naked eye, even in densely light polluted areas such as London. But it did have one downside. At dusk, it was low on the northern horizon where it was predominantly hidden by the fading light from the Sun. For the best chance to see it, observers had to wait until the darkest part of the night, by which time NEOWISE had climbed into a more favourable position in the sky and twilight had mostly faded. In the UK, this happened in the hours just after midnight. So if you wanted to see it, you had to be prepared to stay up late or get up early. Very early.
NEOWISE isn’t set to return for approximately 6,800 years. At aphelion, astronomers think it will be 710 Astronomical Units away from the Sun – which is more than fourteen times Pluto’s aphelion distance, far out beyond the Heliopause. These mind-boggling distances and timescales made NEOWISE an astronomical event I didn’t want to miss.
My first view was brief; a glimpse between clouds at 3am. I went out again the next morning, setting my alarm for 2.30am. Living in a valley makes it difficult to see the sky in is entirety, particularly to the north, as the lower expanse is blocked by a woodland that grows on top of a hill. To see NEOWISE meant I had to drive elsewhere. As the local Tawny Owls called to each other I got into my car and headed south. I had a composition in mind for a photograph on the outskirts of Bridport, with the well known local landmark of Colmers Hill in the foreground. The road dipped lower, passing through my local town, before steadily rising up to meet the main road to Bridport. At the junction I turned left (east) and gasped. Just above the northern horizon, which had previously been hidden by houses and trees, the sky was glowing blue. Bright, electric blue; like a colossal, elaborate graffiti tag. To the east of this, tail spewing like the liquid from a shaken bottle of champagne, was NEOWISE. I was utterly awe-struck. Astrophotographer Alyn Wallace* was also out that morning, and his reaction to seeing the same noctilucent clouds can be seen here. Skip his video along to 8.26 and watch his response – it encapsulates my sentiments exactly.
The limited car park near Quarr Hill, which overlooks Colmers Hill, was packed. Clearly I wasn’t the only photographer with this composition in mind. I squeezed my car into the only gap I could find (thank goodness it was small) and clambered out from the passenger side through a barely open door. I ran, quickly, up the track. As I approached the summit I noticed a collection of lights coming from the head torches and cameras of other photographers.
I turned around and ran back to my car, over the road and up a hill on the other side. Photography, for me, is a solitary pursuit, and the group on Quarr Hill was too much, especially in the fragile hours before dawn. From my new vantage point NEOWISE was badly positioned for my original composition idea, but the noctilucent clouds were well placed, floating behind the silhouette of Colmers Hill – a lone bump in the darkness crowned by nine pines.
My next memorable sighting was on the 15th June 2021. I woke up in the night and decided to head out. I drove to a high vantage point and experienced a mind-boggling display of noctilucent clouds. They stretched across the horizon and into the south of the sky; a huge show. These clouds ordinarily form over the poles, and can only be seen between 45ºN and 80ºN (and equivalent latitudes in the southern hemisphere) so to have them reaching into the south of the sky was exceptional. It does happen sometimes – they’ve been reported from Las Vegas and Los Angeles in the past, but they tend to be confined to higher latitudes.
If you want to see noctilucent clouds for yourself, my advice is to get used to staying up late or waking up abnormally early. In the UK, they can only be seen during the summer, in May, June and July, when the Sun is less than or equal to 6º below the horizon. Wait about an hour after sunset, then look north or, if you prefer, get up at 2am. Be careful not to confuse cirrus clouds illuminated by light pollution with NLCs – although once you’ve seen them, it’s doubtful you’ll make the same mistake again. As they form over the poles, they tend to be fairly low on the horizon, so make sure your view north is not obscured by buildings or trees. What you will see, if there’s a display, is wispy clouds, often with ripples and wave-like structures, that seem to be glowing. They vary in form, density, scale and colour, but it’s their shining quality that gives them away.
Even though they’re a symptom of our changing climate, noctilucent clouds are a beautiful sight, as shown in this video, and certainly worth losing sleep over if we get an extensive display. Be sure to use the hashtag #NLCnow on Twitter to search other people’s sightings or tweet about your own. There’s also a useful Facebook page for noctilucent cloud hunters called Noctilucent clouds around the world, which is regularly updated with the latest sightings and excellent photographs of these ethereal clouds.
*Alyn Wallace sadly passed away on the 28th March, 2024. He was 34 – much too young for such a shining star.
If you liked reading this, and would like to help me keep writing, please consider buying me a coffee via my Ko-fi page. Thank you.