July 22, 2014
Meteoroids Hitting Earth and Moon
image by Astrofotograf Göran Strand, Sweden
Many sky observers have never seen a noctilucent cloud. Having lived in North Dakota for what seemed like 10 years of winter I did get to see NLCs, as well as aurora, and beautiful sky vistas - if only something could be done about the air temperature. But I digress. NLCs have become brighter and more common at lower latitudes during the last decade. In recent weeks European observers have seen spectacular displays, such as this one that Göran captured from Sweden. The clouds form so high - about 80-85 km up, that there is normally little water to make cloud droplets. But extra water is being made in the upper atmosphere because of global warming. The methane (CH4) released from various human activities, as well as coming out of warming permafrost, rises to the upper altitudes where the four hydrogen atoms are stripped from the carbon, and then bond with oxygen to create water. The beauty of the blue wispy filaments we now see in northern skies is another manifestation of our rapidly changing climate (which everyone in the world understands is real except American Republicans - oops, another digression). Even with water up high in the atmosphere it is hard to form droplets and hence clouds. Volcanic debris from powerful eruptions can be nucleation centers, facilitating drop formation. And recent studies have identified meteoroid dust in NLC droplets, indicating that cosmic debris can also provide nucleation points. So on the Moon, small comet debris smashes onto the surface, making a momentary flash and meter-size impact craters. In the Earth's highest atmosphere the comet dust slows and makes friends with some water molecules to create clouds illuminated by the Sun, long after it sets and stops illuminating normal meteorological clouds. The same input produces different results on different worlds.
Nikon D800E at 135mm, f/4.0, ISO 100, Exposure time 0.7 sec. Lens used - Nikon 70-200/2.8
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Yesterday's LPOD: A New One
Tomorrow's LPOD: Who Made This Map?