START OF THE 2025 NOCTILUCENT CLOUD SEASON! 💙

As the aurora season slowly draws to an end (due to longer days, shorter nights and endless twilight skies), we are now entering the 2025 Noctilucent cloud season. 

For many astronomers and Aurora chasers 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 phenomenon that slowly becomes visible over these bright months – Noctilucent Clouds (NLC).

Noctilucent Clouds are stunning natural phenomena to witness and are often what Aurora hunters, astronomers and 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 45-80 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 may not be long now until some of us are treated to our first NLC sightings of the year and there have in fact been reports of possible sightings recently. 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…

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 +45° and +80°.

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. 

The first recorded sightings of Noctilucent Clouds date back to 1885 when amateur astronomers in the German town of Bad Kissingen spotted a new type of mysterious cloud that appeared to shine in the night. This brand new type of cloud became known as Noctilucent Cloud.

It is thought that this first recorded sighting of NLC may be related to the great volcanic eruption of Krakatoa in August 1883. The eruption of Krakatoa released vast amounts of ash, dust and water vapour into the atmosphere. Some researchers believe that the ash and dust particles along with the water vapour that was released into the atmosphere from the Krakatoa eruption may have been the cause for the formation of the first recorded NLC that were seen two years later in 1885.

Ever since that first sighting in 1885 people have been observing and studying these mystical night shining clouds. NLC continue to be a subject of scientific debate and studies have shown a large increase of sightings in recent decades.

Data gathered over a 40-year period from the mid 1960’s to the mid 2000’s has shown a large increase in NLC sightings. Computer simulations modelling the Earth’s atmosphere from the 1870’s to the mid 2000’s have also shown an increase in NLC formation.

Noctilucent Clouds used to be a very rare sight at our latitudes, only being visible near the North and South poles where the conditions for their formation are more likely. However, they have become a much more common sight further down into mid latitudes.

It is known that three things are needed for the creation of NLC, dust particles in the mesosphere for condensation and ice to form around, water to be present in the often extremely dry conditions of the mesosphere, and extremely cold temperatures to cause the small amounts of water in the mesosphere to freeze.

However, nobody knows exactly what particles are responsible for NLC and why they have become a more common sight at lower latitudes. NLC have been a great topic of discussion in the scientific community and there are several plausible theories on what particles cause NLC formation and why they have become a more common sight.

One theory suggests that NLC’s are caused by tiny meteoric 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 and material into our atmosphere that were not previously present, which may be adding to the formation and frequency of NLC.

Another theory into why NLC sightings have been more frequent in recent years was that NLC formation is related to the Sun’s 11 year cycle. However, more recent research has not been able to find any correlation between Solar cycles and the increase in NLC sightings.

Increased NLC activity has also influenced another highly agreed upon theory. Many researchers believe that NLC formations may be linked to and are an indication of global warming and climate change. The reasoning behind this is that increased temperatures at lower tropospheric altitudes result in decreased temperatures in the mesosphere, inducing nucleation (the process of ice crystal formation), resulting in NLC formation.

Research showing increased levels of the greenhouse gas carbon dioxide in the troposphere (which contributes to the warming of the troposphere) support this. Further to this, data from ESA’s GOSAT satellite has shown there to be a year-on-year increase in Methane (another greenhouse gas) concentrations around the world. When Methane reacts with ultra-violet radiation from sunlight, water vapour is formed. This increase in water vapour coupled with a colder mesosphere increases the chance of NLC formation.

General scientific opinion is that climate change is a very likely cause for the increase in NLC formation, however the correlation has not been established conclusively and there is still much to learn about these special clouds.

Whatever the cause, it's definitely worth taking a chance at trying to view these beautiful clouds over this spring and summer season, as despite the trend of increased NLC sighting over the last few decades, we could find that the chance of sightings may begin to decrease and NLC become a much rarer sight in our skies.

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

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.

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 (“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 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 below you can see recent radar images from OSWIN and MAARSY and photographic diagrams from Night Sky Hunter (many thanks to Martin McKenna 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 and we’ve been hooked ever since!  

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

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