Light travels at a speed that is imperceptible to our eye. Yet it is possible to measure and calculate the duration of even the shortest light beam. The project "Celeritas" (Latin, meaning swiftness) consists of a wooden cabinet enclosing a chalkboard printed with white letters reading: "These words are illuminated by light that has traveled a duration of ___ minutes & ___ seconds." The cabinet may be exhibited near a window admitting natural daylight, or under a directed artificial light-source. When the work is installed the distance between the light source and the cabinet is measured and divided by the speed of light (299,792,458m/second) to calculate the duration. The resulting time is written with chalk on the board. If the piece is shown under natural light and the exhibition space is open after nightfall the cabinet doors are closed to prevent the statement from becoming false. When the exhibition ends the calculation is erased. In physics and astronomy "c" denotes the physical "constant" speed of light (as in Einstein’s equation E=mc²). However, Isaac Asimov, in a 1959 essay, asserted that the Latin word “celeritas” is the origin of "c." Viewing the project, our sense of time shifts with regard to the present moment. We find ourselves contemplating the limits of our temporal perception, perhaps reminded that our lives unfold somewhere between seemingly instantaneous light speed and imperceptibly slow geological time.