In Music for a Quarry by Walter Fähndrich, clear tones call across the natural amphitheater of the Hoosac Marble Quarry from ten speakers, equally spaced along its circumference, for fifteen minutes of twilight every evening. Working with the latitude and longitude of the quarry, a computer program begins the music at the same solar time (rather than clock time) each night. The start time (near 8 or 9pm in summer, near 4pm at the winter solstice) changes as the spatial relationship between the earth and sun changes. The first tone appears at the precise moment of astronomical sunset, a moment that is both permanently fixed and changing daily. During this fifteen-minute period, the burden of comprehending the physical space shifts slowly from the eye to the ear as the sounds are traced to their sources.