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Credit & Copyright: Peter Simmering
Explanation:
Sometimes it's night on the ground but day in the air.
As the Earth rotates to eclipse the Sun,
sunset rises up from the ground.
Therefore, at sunset on the ground, sunlight still shines on
clouds above.
Under usual circumstances, a
pretty sunset
might be visible, but unusual
noctilucent clouds float so high up they
can be seen well after dark.
Normally too dim to be seen,
they may become
visible just after sunset during the summer when illuminated by sunlight from below.
Noctilucent clouds
are the highest clouds known and thought to be part of
polar mesospheric
clouds.
Featured here as they appeared two weeks ago,
a network of
noctilucent clouds was captured not only in the distant sky but in reflection
from a small lake just north of
Zwolle,
Netherlands, with trees in stark
silhouette across the horizon.
Unusually bright
noctilucent clouds continue to appear over much of northern
Europe.
Much about
noctilucent clouds has been discovered only over the past decade,
while how they form and evolve remains a
topic of active research.
Gallery:
Recent
noctilucent clouds over Europe
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NASA Web Site Statements, Warnings, and Disclaimers
NASA Official: Jay Norris. Specific rights apply.
A service of: LHEA at NASA / GSFC
& Michigan Tech. U.
Based on Astronomy Picture
Of the Day
Publications with keywords: noctilucent clouds - sunset
Publications with words: noctilucent clouds - sunset
See also: