August 11, 2021
On the day you were born, the universe was already ancient beyond measure — and yet, in all those billions of years, it had never once...
Mammatus Clouds over Saskatchewan
Birthday · August 11, 2021
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APOD published August 11, 2021. Credit: Michael F Johnston. A publication-date match, not a photo taken on your date. Independent of NASA.
When do cloud bottoms appear like bubbles? Normally, cloud bottoms are flat. This is because moist warm air that rises and cools will condense into water droplets at a specific temperature, which usually corresponds to a very specific height. As water droplets grow, an opaque cloud forms. 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. Resulting mammatus clouds can appear especially dramatic if sunlit from the side. The mammatus clouds pictured here, lasting only a few minutes, were photographed over Regina, Saskatchewan, Canada, just after a storm in 2012. Meteor Shower Tonight: Peak of the Perseids
Image credit: Michael F Johnston