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.
But it's not the
end of the world, nor is it the beginning of a fine friendship with alien
neighbours.
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.
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.
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.