NASA's Terra satellite took this picture of an eddy 800 kilometers south of South Africa. Shown in true color, the eddy appears a lighter blue than the surrounding waters because of the microscopic ocean life -- plankton, mostly -- swirling within it. The eddy is 150 kilometers wide. Eddies, Dennis McGillicuddy, an oceanographer at the Woods Hole Oceanographic Institution, are "the internal weather of the sea." As the eddies tumble, they bring nutrients from deep below, allowing for a bloom of life in parts of the ocean that are typically barren.
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Rebecca J. Rosen is a senior editor at The Atlantic, where she oversees coverage of American constitutional law and government in the Battle for the Constitution series.