Discover the cosmos! Each day a different image or photograph of
our fascinating universe is featured, along with a brief
explanation written by a professional astronomer. 2006 July 18
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. Recent
evidence indicates that at least some noctilucent clouds result
from freezing water exhaust from Space Shuttles. Authors &
editors: NASA Web Site Statements, Warnings, and Disclaimers
NASA Official: Jay Norris. Specific rights