Astronomy Picture of the Day

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.

2004 June 7
See Explanation.  Clicking on the picture will download
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Mammatus Clouds Over Mexico
Credit & Copyright: Raymundo Aguirre

Explanation: When do cloud bottoms appear like bubbles? 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. The above mammatus clouds were photographed last month over Monclova, Mexico.

News flash: Rare transit of Venus across the Sun tomorrow
Tomorrow's picture: venus crosses the sun

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