NASA's Aqua satellite was launched on May 4, 2002 with six Earth-observing instruments on board. Aqua circles the Earth every 99 minutes and is in a polar orbit, passing within ten degrees of each pole on every orbit. The orbit is sun-synchronous, meaning that the satellite always passes over a particular part of the Earth at about the same local time each day. Aqua always crosses the equator from south to north at about 1:30 PM local time. One of the instruments on Aqua, MODIS, measures 36 spectral frequencies of light reflected off the Earth in a 2300-kilometer wide swath along this orbit, so that MODIS measures almost the entire surface of the Earth every day. This animation shows the Aqua satellite orbiting for one day, August 27, 2005, showing a set of MODIS measurements taken that day that have been processed to look like a a true-color image of the Earth. Notice that MODIS only takes data during the dayside part of the orbit because it measures reflected light from the Sun, and that there is a bright band of reflected sunlight in the center of swaths over the ocean. Also visible in this animation are Hurricane Katrina, just to the west of Florida in the Gulf of Mexico, and Typhoon Talim, in the westerm Pacific between Japan and New Guinea.
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