February 20, 2011
Somewhere between the hydrogen and the starlight, between the gravity and the grace, the universe conspired to bring you into being.
Mammatus Clouds Over Olympic Valley
Birthday · February 20, 2011
A little universe, just for you
Your date.
Ready to give.
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APOD published February 20, 2011. Full image credits are on the original APOD entry below. A publication-date match, not a photo taken on your date. Independent of NASA.
What's happened to these clouds? Normal cloud bottoms are flat because moist warm air that rises and cools will condense into water droplets at a very specific temperature, which usually corresponds to a very specific height. After water droplets form that air becomes an opaque cloud. Under some conditions, however, cloud pockets can develop that contain large droplets of water or ice that fall into clear air as they evaporate. Such pockets may occur in turbulent air near a thunderstorm, being seen near the top of an anvil cloud, for example. Resulting mammatus clouds can appear especially dramatic if sunlit from the side. These mammatus clouds were photographed last August over Olympic Valley, California, USA.