Not so long ago, an enormous fiery cloud in the skies above Russia could only mean one thing: The beginning of something very very bad indeed.
At the height of the Cold War, a vision like this would set off screams of terror and mass panic, rather than the soft gasps of wonder and awe-struck conversation that can be heard in the YouTube clip of this spectacular phenomenon.
Glider pilots, on the other hand, find lenticular clouds a welcome sight, because wave lift can produce high altitudes and long distances.
The clouds are formed by stable but moist air which has travelled across the Pennines, causing a standing wave to become established.
Lenticular clouds are said to be the single biggest explanation for UFO sightings across the world.
Bright colors (called Irisation) are sometimes seen along the edge of lenticular clouds.
These clouds have also been known to form in cases where a mountain does not exist, but rather as the result of shear winds created by a front.
At the height of the Cold War, a vision like this would set off screams of terror and mass panic, rather than the soft gasps of wonder and awe-struck conversation that can be heard in the YouTube clip of this spectacular phenomenon.
But it's not the end of the world, nor is it the beginning of a fine friendship with alien neighbours.
Duck and cover: Footage of the towering glowing cloud over an unidentified city in Russia has hit YouTube. It is a brilliantly back-lit version of lenticular cloud, often known as a UFO cloud... for obvious reasons
Footage of the glowing circular formation - which hit YouTube yesterday - is one of the most stunning examples of a 'lenticular cloud'.
For obvious reasons, these rare cloud formations are also known as 'UFO clouds' - because of their spooky resemblance to the space ships we are all expecting to imminently arrive in the skies above us.
Sci-fi films as far back as Close Encounters Of The Third Kind (1977) - and more recently Independence Day (1996) - have depicted aliens camouflaging their craft in boiling cloud formations.
Natural beauty: Captured at just the right time, when the sun is striking the bottom of the cloud and the 'halo' above it is created by refracted light, the cloud takes on an eerie appearance
Ribbon of light: A close-up detail of the cloud shows the various shades of light shining through the formation. Lenticular clouds are formed when moist air rises and falls over a mountain or mountain range
But this is little more than the wonder of nature creating an amazing sight.
The footage was taken in an unidentified city in Russia, and voices can be heard marveling at the awesome sight. You don't need to speak Russian to get the gist of the conversation.
What sets this footage apart from other examples of lenticular formations is the amazing glowing nature of the cloud.
Neither of these (as far as we know): Sci-Fi films like Independence Day (1996) like to show aliens disguising their spacecraft as boiling cloud formations, above left, while French nuclear tests in the Pacific Ocean produced similar glowing clouds
Captured just at the right moment, when the sun is directly striking the bottom of the cloud - and light is refracted through the top of the cloud - it gives an amazing two-tone effect.
Lenticular clouds are usually formed by moist air rising over a mountain or range of mountains, forming standing waves of clouds as the air descends again.
The clouds are usually formed perpendicular to the direction of the airflow, and are usually avoided by aircraft pilots because of the turbulence associated with them.
UFO in the UK: This lenticular cloud caused a stir when it was spotted above Farsley in West Yorkshire last year
The clouds are formed by stable but moist air which has travelled across the Pennines, causing a standing wave to become established.
Lenticular clouds are said to be the single biggest explanation for UFO sightings across the world.
Bright colors (called Irisation) are sometimes seen along the edge of lenticular clouds.
These clouds have also been known to form in cases where a mountain does not exist, but rather as the result of shear winds created by a front.
Hovering 'UFO': The cloud spotted in Farsley in West Yorkshire, are most commonly sighted in the Himalayas, Andes and Rocky Mountains, but are very rare in the UK
Unrivalled beauty: Multiple lenticular clouds make for an awesome sight. Their appearance in an otherwise clear sky have been behind many reported UFO sightings
