UT1UT4

UT1UT4 is a speculative term used to describe a dual-component timekeeping scheme that couples UT1, the astronomical time scale tied to Earth's rotation, with a hypothetical UT4 component. In this framework, time is represented by two coordinates: UT1, which tracks the immediate rotation angle of the planet, and UT4, a four-parameter model intended to capture slower, long-term variations in rotation rate and orientation. The "4" in UT4 is a reference to the model's four coefficients, which could in principle account for secular changes, tidal accelerations, polar motion, and nutation over extended periods.

In proposed implementations, a UT1UT4 timestamp would be written as a pair, such as 12:34:56.789 UT1 / 2025.1234 UT4, or more compact forms separating the components with a delimiter. Applications would include high-precision astronomical observations or simulations requiring both real-time rotation and long-term dynamics. UT4 is envisioned as a separate time axis that progresses at a different rate than UT1, allowing parallel tracking of instantaneous Earth-rotation state and a modeled long-term evolution.

UT1UT4 is not an official standard and is not maintained by timekeeping organizations such as the International Bureau of Weights and Measures or the International Astronomical Union. It appears mainly in speculative literature, thought experiments, or education to illustrate the idea of multi-parameter time scales. In contrast, real-world systems rely on UTC with UT1 approximations for solar-time alignment.

See also UT1, UT2, UTC, universal time, time scales, astronomical timekeeping.