June 19, 2005
A birthday is what happens when cosmic time briefly puts down the scale of eons and pays attention to a single human year.
Noctilucent Clouds
Birthday · June 19, 2005
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APOD published June 19, 2005. Credit: Pekka Parviainen (Polar Image). A publication-date match, not a photo taken on your date. Independent of NASA.
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, a network of noctilucent clouds casts a colorful but eerie glow visible above the dark. 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.
Image credit: Pekka Parviainen (Polar Image)