cadence

The term cadence is often used for the period (or frequency) of periodic observations. It may roughly match the time interval between observations, e.g., when a 5-second observation is made every 30 minutes. Alternately, it may roughly match the exposure time of individual "snapshots", in the case where something is being observed continuously, but data (e.g., CCD "counts") is stored periodically. This use of the term is common when transients are being searched for or observed, such as transits, gravitational microlensing, or radial-velocity indications. Such a search with multiple target-types and goals (e.g., the Rubin Observatory), an elaborate multiple-hierarchy cadence (essentially guidelines for how its use will be scheduled, including periodic operations) may be planned, based upon numerous criteria. Rubin's aims at monitoring much of the sky at regular intervals, with time-slots devoted to followup, to frequent monitoring of select survey fields, and to monitoring newly discovered transients and solar system objects of high interest.

The term mean cadence is often used in describing surveys that are loosely periodic, which is common for long-term (days/weeks/months) light curve observation, such as those of supernovae: the survey's mean cadence might well be some number of days. Over such a long term, telescope availability and weather often make exact periodicity impractical.