July 18, 2006
Somewhere between the hydrogen and the starlight, between the gravity and the grace, the universe conspired to bring you into being.
Noctilucent Clouds Over Sweden
Birthday · July 18, 2006
A little universe, just for you
Your date.
Ready to give.
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APOD published July 18, 2006. Full image credits are on the original APOD entry below. 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 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.