Today, the U.S. Naval Observatory (USNO) is best known to most Americans as the location of the vice president's residence. Asked to search their memories, a few may recall that USNO maintains the nation's master clock, and is in some way responsible for introducing a “leap second” on New Year's Eve every few years. Even in the scientific community, the USNO is best known and most highly regarded for its service as the nation's timekeeper.

In Sky and Ocean Joined: The U.S. Naval Observatory, 1830–2000, Steven Dick points out that the history of the development of ever-more accurate clocks and the dissemination of time closely parallels the general advance of science and technology. In addition, he takes the reader inside USNO to meet some of the more fascinating individuals that drove the events and scientific achievements associated with the work of maintaining the nation's master clock.