Time domain science forms an increasing fraction of astronomical programs at many facilities. Synoptic and targeted observing modes of transient, varying, and moving sources rely on precise clocks to provide the underlying time tags. Often precision is mistaken for accuracy, or the precise time signals never reach the instrumentation in the first place. We will discuss issues of deploying a stable high-precision GNSS clock on a remote mountaintop, and of conveying the resulting time signals to a computer in a way that permits hardware timestamping of the camera shutter (or equivalent) rather than the arbitrary delays encountered with non-real-time data acquisition software. Strengths and limitations of the Network Time Protocol will be reviewed. Timekeeping infrastructure deployed for the Catalina Sky Survey will serve as an example.
The Catalina Sky Survey (CSS) at the University of Arizona has discovered 47% of all known near-Earth objects (NEOs) and contributed 59 million observations to the Minor Planet Center.<sup>,</sup> CSS operates three telescopes fulltime, two of which primarily survey for new moving objects and one that follows up specific objects, particularly recent discoveries that may be NEOs. To be as efficient and effective as possible, CSS developed a flexible queue manager that enables all of our telescopes to perform both survey and follow-up observations as needed. The rate of discovery of new NEOs has increased greatly over the years, requiring a quantity of follow-ups that can only be accomplished with automated observing coordinated by a queue manager. Imaging moving targets also adds complexity, particularly the need for proper time intervals between images or the use of “track and stack” observing, necessitating that observations of multiple moving objects be properly interleaved in time. Targets are also added to and removed from the queue throughout the night when new discoveries are made or when objects are followed up by other telescopes. The CSS queue manager addresses all these challenges.