This new image of the Earth at night is a composite assembled from data acquired by the Suomi National Polar-orbiting Partnership (Suomi NPP) satellite over nine days in April 2012 and thirteen days in October 2012. It took 312 orbits and 2.5 terabytes of data to get a clear shot of every parcel of Earth’s land surface and islands.
The nighttime view of Earth was made possible by the “day-night band” of the Visible Infrared Imaging Radiometer Suite. VIIRS detects light in a range of wavelengths from green to near-infrared and uses filtering techniques to observe dim signals such as gas flares, auroras, wildfires, city lights, and reflected moonlight.
Away from the cities, much of the nightlight observed by Suomi NPP is wildfire. In other places, fishing boats, gas flares, lightning, oil drilling, or mining operations can show up as points of light. The number of rural lights is also a function of composite imaging.
Fires and other lighting could have been detected on any one day and integrated into the composite picture even though they were temporary. That seems to be the case in central and western Australia, where many lights appear in this map. Different areas burned with wildfire at different times that the satellite passed over, giving the impression (in the composite view) that the entire area was lit up at once.