TDT

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Definition

Noun: 1. Terrestrial Dynamical Time: A precise astronomical time scale. It is a theoretical uniform time based on the orbital motion of the Earth around the Sun, used for calculating the positions of celestial bodies. It is essentially the modern successor to Ephemeris Time (ET).

Usage

TDT is a specialized scientific term used almost exclusively in the fields of astronomy, astrophysics, and celestial mechanics. It is used to refer to a specific, highly accurate time system that accounts for the irregularities in Earth's rotation.

Examples
  • Astronomers used TDT to calculate the precise moment of the solar eclipse.
  • The satellite's ephemeris was generated using Terrestrial Dynamical Time.
  • For high-precision calculations, the difference between TDT and Universal Time must be considered.
Advanced Usage
  • TDT was officially defined in 1991 by the International Astronomical Union. It is now formally known as Terrestrial Time (TT), but the term TDT is still commonly used and understood in historical and technical contexts.
  • The key characteristic of TDT is that it is a uniform time scale, unlike time scales based on the actual, variable rotation of the Earth.
Variants and Related Words
  • TT (Terrestrial Time): The modern, official name for the time scale previously called TDT.
  • Ephemeris Time (ET): The predecessor to TDT.
  • Universal Time (UT): A time standard based on Earth's rotation, which is irregular and differs from TDT.
  • International Atomic Time (TAI): The primary international time standard from which TDT/TT is derived by adding a fixed offset (32.184 seconds).
Synonyms
  • Terrestrial Time (TT)
Noun
  1. (astronomy) a measure of time defined by Earth's orbital motion; terrestrial time is mean solar time corrected for the irregularities of the Earth's motions

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