ephemeris time: meaning, definition, pronunciation and examples
Very rareSpecialist / Technical
Quick answer
What does “ephemeris time” mean?
A former standard astronomical time scale based on the orbital motion of the Earth around the Sun.
Audio
Pronunciation
Definition
Meaning and Definition
A former standard astronomical time scale based on the orbital motion of the Earth around the Sun.
In historical astronomy and timekeeping, it refers to a uniform time defined by the laws of dynamics and the motion of celestial bodies, superseded by Terrestrial Time (TT) and other modern time scales.
Dialectal Variation
British vs American Usage
Differences
No significant differences in usage, spelling, or definition between UK and US English in this technical term.
Connotations
Technical, historical, precise, obsolete.
Frequency
Equally rare in both national varieties.
Grammar
How to Use “ephemeris time” in a Sentence
[Noun] is expressed in ephemeris time.They calculated [Noun Phrase] using ephemeris time.Vocabulary
Collocations
Examples
Examples of “ephemeris time” in a Sentence
verb
British English
- (Not applicable - noun phrase)
American English
- (Not applicable - noun phrase)
adverb
British English
- (Not applicable - noun phrase)
American English
- (Not applicable - noun phrase)
adjective
British English
- The ephemeris-time calculation is archived in the observatory's records.
Usage
Meaning in Context
Business
Not used.
Academic
Used in historical astronomy papers and textbooks discussing the evolution of time standards.
Everyday
Not used.
Technical
Used in precise historical references in astronomy, satellite tracking (historical data), and geodesy.
Vocabulary
Synonyms of “ephemeris time”
Strong
Neutral
Weak
Vocabulary
Antonyms of “ephemeris time”
Watch out
Common Mistakes When Using “ephemeris time”
- Confusing it with 'ephemeral time' meaning short-lived time.
- Using it to refer to modern time standards.
- Pronouncing 'ephemeris' with emphasis on the third syllable.
FAQ
Frequently Asked Questions
No, it is obsolete. It was officially replaced in the 1970s and 1980s by Terrestrial Time (TT) and other time scales derived from International Atomic Time (TAI).
It was based on the mean orbital motion of the Earth around the Sun as described by Newcomb's tables of the Sun, making it a dynamical time scale.
Astronomers, astrophysicists, and specialists in celestial mechanics and satellite tracking used it during its period of official use (c. 1960-1984).
Universal Time is based on the Earth's rotation, which is irregular. Ephemeris Time was designed as a uniform, dynamically defined time scale to eliminate these rotational irregularities for precise calculations.
A former standard astronomical time scale based on the orbital motion of the Earth around the Sun.
Ephemeris time is usually specialist / technical in register.
Ephemeris time: in British English it is pronounced /ɪˈfɛmərɪs taɪm/, and in American English it is pronounced /ɪˈfɛmərɪs taɪm/. Tap the audio buttons above to hear it.
Phrases
Idioms & Phrases
- “(No common idioms use this term)”
Learning
Memory Aids
Mnemonic
Think: 'E-phemeris' like 'Ephemeral' (lasting a short time), but it's actually a long-term, precise measure of time based on planet paths.
Conceptual Metaphor
Time as a Path of Celestial Bodies.
Practice
Quiz
Ephemeris Time (ET) was primarily superseded by which standard?