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.
Pictured above
last month, a network of
noctilucent clouds cast a colorful but eerie glow after dusk near
Vallentuna,
Sweden.
Although
noctilucent clouds are thought to be composed of
small ice-coated particles,
much remains unknown about them.
Satellites launched to help study these clouds includes Sweden's
Odin and NASA's
AIM.
Recent evidence indicates that at least some
noctilucent clouds result from freezing water exhaust from
Space Shuttles.
