Noctilucent Clouds
On summer nights, from specific latitudes, an awe inspiring atmospheric phenomena can sometimes be observed. Their visibility varies from extremely faint and practically unrecognisable to vast tracts of multi coloured, delicately structured clouds covering the sky like a priceless tapestry and shining with a unique, unforgettable light.
These "summer sky sailors" are known as Noctilucent Clouds
or NLC. "Noctilucent" is a Latin derivative which, loosely translated,
means "night shining", hence NLC are night shining clouds, a
very good description. Although the latter part of the nomenclature implicitly
states that the phenomena are clouds they bare little resemblance to the
common weather clouds with which we are all familiar. These clouds are
much, much more unique, this just being one of the many facets which make
NLC such an engrossing and beautiful phenomena to observe and understand.
NLC are visible during the summer months of each hemisphere, mid-May to
mid-August in the Northern Hemisphere and mid-November to mid-February
in the Southern Hemisphere but only from a specific latitudinal zone.
This zone is 50-65° North or South, with 57° being the best latitude
to observe NLC from. June and July and December and January are the best
months to observe NLC for each respective hemisphere.
South of 50° and the sky is too dark, due to the sun being more than 12° below the horizon (astronomical twilight) and north of 65° and the sky is too light as the sun is less than 6° below the horizon (civil twilight).
Noctilucent Clouds - A fine sight during summer months
The visibility of NLC is due to their great altitude. Their altitudes have been accurately determined by ground based parallactic photography and in-situ rocket measurements. The clouds reside at an altitude of 80-85Km with an average altitude of 83Km.
The vast majority of NLC observers are amateurs due to the fact that justification
of an extended program of scientific study is very difficult because of
the visibility and altitude of NLC.
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