It comes from the 2016 New World Atlas of Artificial Night Sky Brightness, not from a survey in which billions of people were asked to look up. Its headline results were stark: more than 80 percent of the global population lived under light-polluted skies, while more than 99 percent of people in the United States and Europe did. The number has remained in circulation because the atlas is still the most complete population-weighted global estimate of this specific loss. The authors explicitly noted that the sample did not represent the average distribution of either land area or global population. The defensible statement remains precise: the best global atlas found that more than a third of humanity lived where artificial skyglow hid the Milky Way under its modeled conditions.