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 on position, velocity, gravity, and the finite speed of light. Systems with precise, potentially complex definitions are needed to handle very small sub-second timing and the multiple frames of reference involved in astronomy and spacecraft. The systems generally count off SI seconds, but cannot remain in sync, often being out of sync by seconds. Examples:

The International Astronomical Union defines and standardizes time systems for use in astronomy. Before its current systems were developed, similar systems were in use, generally taking fewer factors into account or otherwise flawed. Among them were ephemeris time (Teph) and terrestrial dynamical time (TDT or TD).


(time,physics,relativity)
Further reading:
https://en.wikipedia.org/wiki/Time_standard
https://en.wikipedia.org/wiki/Barycentric_Dynamical_Time
https://en.wikipedia.org/wiki/Terrestrial_Time
https://en.wikipedia.org/wiki/Universal_Time

Referenced by pages:
astronomical catalog
epoch B1950.0
Julian date (JD)
photographic zenith tube (PZT)
pulsar timing array (PTA)
solar time
Terrestrial Time (TT)
timescale (t)

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