terrestrial time
A scientist uses terrestrial time to calculate the precise moment of a solar eclipse.
Terrestrial Time (noun): 1. A precise astronomical time scale: Terrestrial Time (TT) is a modern astronomical time standard. It is a theoretical uniform time scale defined on the Earth's geoid (mean sea level). It represents the proper time of a clock at rest on the Earth's surface, flowing uniformly without the irregularities found in solar time. 2. A corrected measure of Earth's motion: It is derived from the concept of Ephemeris Time but is more precisely defined. TT accounts for and corrects the irregularities in the Earth's rotation and orbital motion, providing a stable, continuous, and linear flow of time for precise calculations.
Terrestrial Time is used as a precise reference in astronomy, geodesy, and celestial mechanics. * Astronomical Calculations: Ephemerides for planets and spacecraft are typically calculated using Terrestrial Time. * Time Standard Reference: The difference between Terrestrial Time and International Atomic Time (TAI) is a constant offset of 32.184 seconds. * Scientific Context: To compare observations from different epochs, astronomers must convert the recorded times to a uniform scale like Terrestrial Time.
- Relationship to Other Time Scales: Terrestrial Time is the modern successor to Ephemeris Time (ET). It is directly related to International Atomic Time (TAI) by the definition: TT = TAI + 32.184 seconds. It differs from Coordinated Universal Time (UTC) due to leap seconds and from Universal Time (UT1) due to the irregularity of Earth's rotation.
- In Relativity: For the most precise applications (e.g., deep-space navigation), the coordinate time scale Geocentric Coordinate Time (TCG) is used, which runs at a different rate than TT due to gravitational time dilation. TT is defined as a linear transformation of TCG.
- TT: The standard abbreviation for Terrestrial Time.
- Ephemeris Time (ET): The historical predecessor to TT, based on the Earth's orbital motion.
- International Atomic Time (TAI): The primary international time scale based on a weighted average of atomic clocks. TT is defined as TAI plus a fixed offset.
- Geocentric Coordinate Time (TCG): A coordinate time scale in the context of general relativity, used for calculations in the geocentric reference frame. TT is a scaled version of TCG.
- Terrestrial Dynamical Time (TDT): This was the official name for this time scale from 1984 to 1991. In 1991, the name was simplified to "Terrestrial Time" (TT), though the definition remained essentially the same. The terms are often used interchangeably in historical contexts.
- Time Scale: A system for measuring the passage of time. Terrestrial Time is one of several specialized time scales.
- Leap Second: A one-second adjustment that is occasionally applied to Coordinated Universal Time (UTC) to keep it close to mean solar time (UT1). TT does not include leap seconds; it is a continuous scale.
- ΔT (Delta T): The time difference obtained by subtracting Universal Time (UT1) from Terrestrial Time (TT): ΔT = TT − UT1. This value represents the cumulative effect of the slowing of Earth's rotation and is published in astronomical almanacs.
A scientist uses terrestrial time to calculate the precise moment of a solar eclipse.
- (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