Astrophysics (index)about

time standard

(time system, time scale)
(method of designating points in time and quantifying time periods)

A time standard (or time system or time scale, but not "timescale" in the sense of the order-of-magnitude of the time period in which some physical process happens) is a system of designating points in time and quantifying time periods, often in light of relativity and the resulting effects position, velocity, gravity, and the finite speed of light. Such complex systems are needed to handle very small sub-second timing. The systems generally count off SI seconds, but can't be in sync, often being out of sync by seconds. Examples:

The International Astronomical Union defines and standardizes the time systems for and used in astronomy. Before these systems were developed, similar systems, taking fewer factors into account or otherwise flawed have been in use, including ephemeris time (Teph) and terrestrial dynamical time (TDT or TD).


Referenced by:
astronomical catalog
Julian date (JD)
solar time
timescale (t)
terrestrial time (TT)