BEGINNING OF 2024'S NOCTILUCENT CLOUD SEASON!!! 💙

RARE EERY ‘NIGHT SHINING’ CLOUDS SET TO ILLUMINATE OUR SPRING/SUMMER SKIES! THE 2024 NOCTILUCENT CLOUDS (NLC) SEASON IS ABOUT TO BEGIN! 💙

As the aurora season slowly draws to an end (due to longer days, shorter nights and endless twilight skies), we are now entering the 2024 Noctilucent cloud season. 

For many astronomers the summer months can be frustrating. The endless nautical twilight we experience during the late spring/summer months makes deep sky observing, deep sky astrophotography and aurora hunting increasingly difficult. However as the skies get brighter there is another amazing natural phenomena that slowly becomes visible over these bright months.

Noctilucent Clouds are a stunning natural phenomena to witness and are often what aurora hunters, astronomers and deep sky astrophotographers like ourselves turn our focus to in the late spring/summer months.

These beautiful phenomena can be witnessed by any one in northern to mid-northern latitudes (between around 50-65 degrees above the equator) when the conditions are just right. Another great thing about NLC’s is that these beautiful shimmering clouds are often much easier to witness than the often elusive Northern Lights.

It won’t be long now until some of us are treated to our first NLC sightings of the year, there have in fact been reports of recent sightings in Denmark and Germany. These recent sightings have not been confirmed, however confirmed sightings may be imminent.

Both the Middle Atmosphere Alomar Radar System (MAARSY) and the Ostsee Wind Radar (OSWIN) which detect and monitor echoes from the atmospheric region called the mesosphere, have recently observed echoes in the polar mesosphere!

The extremely cold temperatures in the upper atmosphere that are associated with these Polar Mesospheric Echoes are a good indication that the atmosphere is ready for the formation of NLC. Polar Mesospheric Summer Echoes and Noctilucent Clouds are often (but not always) observed at the same time.

Please read on for more information on Noctilucent Clouds AKA ‘night shining clouds’, what they are, and how and when to see them…

WHAT ARE NOCTILUCENT CLOUDS?

The word ‘Noctilucent’ roughly translates to "night shining" in Latin. Noctilucent clouds are very beautiful, eerie, wispy, lace-like, ghostly veils of clouds that often appear to be shimmering in the nights sky for those between the latitudes of around +50° and +65°.

They are created from ice crystals that form around dust particles high up (around and above 200,000ft / 76km) in the Earth’s upper atmosphere (mesosphere) and appear when illuminated by sunlight from the Sun once it has descended more than 6 degrees below the horizon during astronomical twilight.

NLC’s are particularly special because only in late spring/summer, can the mesosphere reach the temperature of -120°C or lower that is required to freeze the small amount of water in the mesosphere, creating the ice crystals that form Noctilucent Clouds. 

When visible, NLC’s put on amazing shows. NLC can display many beautiful patterns, structures and formations, often slowly and gracefully moving and changing as you watch them dance in the twilight sky. Displays can range anywhere from faint subtle glows on the horizon to intense and distinctively pronounced displays that take over the twilight sky. 

Noctilucent Clouds typically appear a white/silvery colour but may show different colours due to the position of the sun creating different atmospheric effects. Sometimes when viewing NLC’s nearer the horizon you may also be able to see red, orange, yellow and green colour tinges. At the very top of a display you may also be able to see a striking blue or purple canopy.

Although movement in NLC can be very difficult to observe to the eye, these clouds are in fact moving at around 400mph. Time-lapse photography can reveal the wonderful movement that NLC’s produce. NLC will always appear to move towards the East, this effect is caused by the Earth’s rotation. One way which could help you observe this gentle movement is by looking at a bright star and seeing how the NLC’s move in relation to the bright star over time.

THEORIES ON WHY NLC OCCUR AND WHY WE HAVE SEEN MORE NLC IN PREVIOUS YEARS

Very little is known about the exact cause of NLC’s, however there are several plausible theories on how they are formed and why they have become a more common sight in previous years.

One theory suggests that NLC’s are caused by tiny meteor dust particles which form ice crystals around them. These particles made from the remnants of meteors, comets and asteroids, are thought to be so small they are likened to smoke particles.

Another theory suggests atmospheric dust from pollution and volcanoes may be the cause for these clouds.

Some believe that an increase in space missions and rocket launches have introduced vast amounts of elements into our atmosphere that were not previously present, which may be the cause of/may be adding to the formation and frequency of NLC.  

Noctilucent Clouds used to be a very rare sight at our latitudes, only being visible near the North and South poles. However, in recent years past they have become a much more common sight further down into mid latitudes. This increased NLC activity has influenced another theory. Some researchers believe that NLC formations may be linked to and are an indication of global warming. The reasoning behind this is that increased temperatures at lower altitudes result in decreased temperatures in the mesosphere, inducing nucleation (the process of crystal formation), resulting in NLC formation.

Another theory which may explain the increased NLC sightings in previous years past is that these ethereal, opalescent clouds may actually be a sign of our recent deep solar minimum. Solar minimum is a period of time when the sun is least active. Solar minimum is also a time where cosmic ray penetration of interstellar space is at it's peak. This increased cosmic ray activity is thought to actually be helping form noctilucent clouds that are much brighter and further into southernly latitudes than we've ever seen before. 

There may be some credence to this last theory as sightings decreased over 2023 compared to previous years, and we are now heading into the middle of the Sun’s most active period in it’s 11 year cycle known as Solar Maximum.

It's definitely worth taking a chance at trying to view these beautiful clouds over this spring and summer season, as if this latter theory is correct, we may start to see even less of these wonderful phenomena as we head into the middle of Solar maximum.

WHAT NOCTILUCENT CLOUDS CAN TEACH US

NLC are sensitive to atmospheric conditions and temperatures. Because of this, they can act as an indicator of information about the wind circulation that causes these temperatures. They can tell scientists that circulation exists and about the strength of this circulation.

Studies have shown that as the climate warms, NLC become more visible and may be an indicator of global warming.

WHERE AND WHEN TO LOOK OUT FOR NLC'S

The best time for being able to spot NLCs in the northern hemisphere, is between late May and mid August with the best sightings being either side of the Summer Solstice. The outlook is encouraging for a fairly good NLC season this year after a few years of great displays. Last season we did see a decline in the frequency of displays. However we were still treated to some lovely Noctilucent Clouds. So it is still worth watching the northern skies from now onwards and throughout summer time if you’d like to see these beautiful clouds.

An hour or two after the sun sets and an hour or two before the sun rises are good times to look out for NLCs. The length of an NLC display may vary, they can be visible for a short amount of time, or all night long! 

These clouds are a stunning sight to behold, and unlike the Aurora Borealis, these special clouds are typically visible to the naked eye, so no need for a camera or any special equipment, just a view to the North. Although usually appearing to the North, NLC may also be visible in the North East to North West too.

NLCs are impossible to accurately predict in advance. This makes them a very special and exciting subject for amateur observers and photographers. Radar images and lidar images can give us an indication of possible activity, but the only way to really know if NLC’s are visible is to go outside and check.

We will do our best to keep you updated about NLC activity on Astro Dog, to let you know if conditions are favourable and report any NLC sightings.

VIEWING TIPS

Make sure you have a clear view to the northern horizon. NLC can also be spotted anywhere above the north-west to north-eastern horizons.

Being in a location free from light pollution can improve your chances of seeing dimmer NLC, although strong NLC shows can be viewed from light polluted towns and cites.

High level Cirrus clouds can easily be mistaken for NLC, especially just after sunset when the low level Sun illuminates these delicate cloud strips with a golden/red colour. You can tell if you are looking at Cirrus clouds by their 'normal' movement and darker profile as the Sun drops lower beneath the horizon. 

NLCs viewed under magnification from binoculars or a telescope differ from Tropospheric (weather producing / “normal”) cloud. Typical clouds will have soft edges with a low contrast dark profile. NLCs are unmistakable, often with distinct complex structures.

NLC are an incredible sight with the naked eye, however if you own a pair of binoculars, try using them for a more closer look at the detail in NLC structures. You can also use binoculars to detect fainter/less obvious NLC that are too dim for the naked eye to discern. 

It is impossible to predict how long a NLC display will last, some may only occur just after sunset and fade out heading into the darker twilight. If you spot some NLC just after sunset which fades away there is also a good/strong possibility of the NLC re-appearing just before sunrise. This fading is caused by the NLC clouds drifting into the Earths umbra (the shadow cast by the Earth) and then being re-illuminated as they drift back into the pre-dawn sunlight.

NLC can make for amazing photographs that are incredibly easy to capture. You don’t need a special camera to capture them and even a simple mobile phone camera can snap great pictures of NLC.

ATTACHED IMAGES

Attached below you can see recent radar images from OSWIN and MAARSY and photographic diagrams from Night Sky Hunter (many thanks to Martin Mc Kenna for these) demonstrating some of the stunning patterns, formations and structures you can see within NLC displays.

We've been hunting NLC for around a decade now and they're a stunning sight to behold. I remember the first time we saw them, it was incredibly exciting and memorable to witness, we’ve been hooked ever since!  

If you head out, good luck, stay safe and clear skies. 💖