On a Wednesday in August, the moon drew its ancient veil across the Northern Hemisphere, plunging a narrow corridor of Earth into brief midday darkness. The path of totality — that rare and fleeting gift — moved from the Arctic wilds of Russia through Iceland and into northern Spain, a country that had not stood in such a shadow since 1905. Some 230 million people across Europe witnessed the sun diminished, if not fully extinguished, and in that shared dimming, humanity was reminded once more that the cosmos operates on timescales that dwarf our own.