Evening ends three times, and each ending belongs to a different trade. When the sun is six degrees below the horizon, civil twilight is over: too dark to read a newspaper outside without a lamp. At twelve degrees nautical twilight ends, the moment a sailor can no longer make out the horizon to measure a star against it. At eighteen the astronomers finally get the sky they were waiting for. The sun is setting about now in Chicago, whose clock this house keeps, and over the next hour and a half the evening will close like a shop shutting one counter at a time, the readers sent home first and the stargazers let in last.