Like the drift of the continents or the erosion of great mountain ranges on Earth, the motion of the stars across the sky is almost imperceptibly small over the paltry span of a human lifetime. But in this quite astonishing video made with data from the European Space Agency’s (ESA’s) Gaia spacecraft, which compresses 5 million years of star motion into a few minutes, you can see more than 2 million stars move across the sky like grains of pollen floating in a breeze. It is mesmerizing (and unexpectedly calming)...