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Earth as a marble: black and blue, now and then

Astronauts aboard Apollo 17 treated the globe to its first full view of itself on 7 December 1972, snapping the iconic Blue Marble photograph after travelling more than 32,000 kilometres in just over five hours. Very nearly 40 years later, scientists on Wednesday treated the world to its latest self portrait — this taken at night and appropriately named Black Marble — at the American Geophysical Union meeting in San Francisco, California.

Blue Marble influenced a generation of scientists and environmentalists and captured the public imagination just as the environmental movement was taking hold (a retrospective from Don Wuebbles, an atmospheric scientist at the University of Illinois at Urbana-Champaign, is available in the latest edition of Eos). It would be hard for a single photograph to have such an impact today (and in this case there is, in fact, no single photograph) but the inevitable buzz about Black Marble nonetheless serves as a nice reminder that such images still have the capacity to inspire curiosity.

Produced using a new high-resolution sensor aboard the United States’ latest polar-orbiting weather satellite, Black Marble provides a nice update to the original Earth at Night map that NASA released in November 2000. A similar composition has been stitched together (to get around the inevitable cloud cover, as well as the spherical nature of the Earth) and is available in a gallery of images and animations on the NASA website, but it is the level of detail available at regional and even local levels that has scientists excited (see the United States and the Nile River Valley).

“It is very high-quality data, with substantially better spatial resolution,” said Chris Elvidge, a scientist with the National Oceanic and Atmospheric Administration (NOAA) National Geophysical Data Center in Boulder, Colorado. Specifically, the new sensor captures data at a resolution of about 750 metres, compared to 5 kilometres for its predecessor. It is also better equipped to process soft light, which means there is detail and definition in areas that were previously washed out with light.

Elvidge and colleagues talked about various scientific uses for the data, which can serve as a proxy for things such as population distribution, economic activity, carbon emissions and the use of fossil fuels. Scientists can use the data to track natural-gas flaring, forest fires and volcanic eruptions as well as auroras and, when the night light is right, clouds, which opens the door to new meteorological applications. And of course the sensor serves other purposes during the day.

“We’ve only scratched the surface,” says Steve Miller, a researcher at NOAA’s Colorado State University Cooperative Institute for Research in the Atmosphere in Fort Collins. “This is a new frontier for science.”



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