Ephemeris Time
E497211
Ephemeris Time is a former astronomical time standard based on the orbital motion of the Earth around the Sun, used to provide a uniform measure of time before being replaced by more precise atomic-based scales.
All labels observed (1)
| Label | Occurrences |
|---|---|
| Ephemeris Time canonical | 3 |
How this entity was disambiguated
This entity first appeared as the object of triple T5150754 — resolving that mention is where its identity was fixed. The disambiguator weighed these candidate entities and picked the highlighted one (or “None”, minting a new entity). This is how homonymy is resolved: the same surface form can point to different entities.
NED1
Entity disambiguation (via context triple)
gpt-5-mini-2025-08-07
Target entity: Ephemeris Time Context triple: [Terrestrial Time, successorOf, Ephemeris Time]
-
A.
Terrestrial Time
Terrestrial Time is a modern astronomical time standard used for precise calculations of planetary motion and ephemerides, defined in relation to atomic time rather than Earth's rotation.
-
B.
Coordinated Universal Time
Coordinated Universal Time (UTC) is the primary global time standard by which the world regulates clocks and time, serving as the basis for most civil time zones.
-
C.
Greenwich Mean Time
Greenwich Mean Time is the mean solar time at the Royal Observatory in Greenwich, London, historically used as the world’s primary reference for timekeeping and the basis for Coordinated Universal Time (UTC).
-
D.
International Atomic Time
International Atomic Time is a high-precision time standard based on the combined output of atomic clocks worldwide, serving as the fundamental reference for modern civil and scientific timekeeping.
-
E.
Metonic cycle
The Metonic cycle is a 19-year astronomical period after which the phases of the Moon recur on the same days of the solar year, forming the basis for many lunisolar calendars.
- F. None of above. chosen
- G. Unsure - the case is ambiguous/there is not enough information to decide.
NED2
Entity disambiguation (via description)
gpt-5-mini-2025-08-07
Target entity: Ephemeris Time Target entity description: Ephemeris Time is a former astronomical time standard based on the orbital motion of the Earth around the Sun, used to provide a uniform measure of time before being replaced by more precise atomic-based scales.
-
A.
Terrestrial Time
Terrestrial Time is a modern astronomical time standard used for precise calculations of planetary motion and ephemerides, defined in relation to atomic time rather than Earth's rotation.
-
B.
Coordinated Universal Time
Coordinated Universal Time (UTC) is the primary global time standard by which the world regulates clocks and time, serving as the basis for most civil time zones.
-
C.
Greenwich Mean Time
Greenwich Mean Time is the mean solar time at the Royal Observatory in Greenwich, London, historically used as the world’s primary reference for timekeeping and the basis for Coordinated Universal Time (UTC).
-
D.
International Atomic Time
International Atomic Time is a high-precision time standard based on the combined output of atomic clocks worldwide, serving as the fundamental reference for modern civil and scientific timekeeping.
-
E.
Metonic cycle
The Metonic cycle is a 19-year astronomical period after which the phases of the Moon recur on the same days of the solar year, forming the basis for many lunisolar calendars.
- F. None of above. chosen
Statements (46)
| Predicate | Object |
|---|---|
| instanceOf |
astronomical time standard
ⓘ
time scale ⓘ |
| accuracyComparedToSolarTime | more uniform than mean solar time ⓘ |
| basedOn | orbital motion of the Earth around the Sun ⓘ |
| category |
astronomy
ⓘ
timekeeping ⓘ |
| conceptDevelopedIn | mid-20th century ⓘ |
| definedBy |
motion of the Earth in its orbit around the Sun
ⓘ
theoretical gravitational motion rather than Earth rotation ⓘ |
| definedIn | 1952 IAU system of astronomical constants ⓘ |
| definedInTermsOf | tropical year 1900 ⓘ |
| definedRelativeTo | Newcomb’s theory of the motion of the Sun ⓘ |
| ephemerisSecondDefinedAs | 1/31,556,925.9747 of the tropical year for 1900 January 0 at 12h ephemeris time ⓘ |
| formalDefinitionYear | 1952 ⓘ |
| frameOfReference | solar system dynamics ⓘ |
| historicalRole | bridge between astronomical and atomic time scales ⓘ |
| introducedBy | International Astronomical Union ⓘ |
| measurementRealization |
lunar observations
ⓘ
observations of planetary positions ⓘ optical and radar observations of planets ⓘ |
| motivation |
achieve a uniform time scale for celestial mechanics
ⓘ
remove irregularities in mean solar time ⓘ |
| precision | suitable for mid-20th-century planetary ephemerides ⓘ |
| redefinitionImpact | led to the modern SI second based on atomic transitions ⓘ |
| referenceBody |
Earth
ⓘ
Sun ⓘ |
| relatedTo |
Barycentric Dynamical Time
ⓘ
Geocentric Dynamical Time ⓘ
linked to:
Geocentric Coordinate Time
International Atomic Time ⓘ Terrestrial Time ⓘ |
| replacedBy |
International Atomic Time
ⓘ
Terrestrial Dynamical Time ⓘ
linked to:
Terrestrial Time
Terrestrial Time ⓘ atomic time scales ⓘ |
| replacedStandard | mean solar time ⓘ |
| standardizedBy | International Astronomical Union ⓘ |
| status | obsolete as a primary time standard ⓘ |
| stillUsedAs | historical reference time scale ⓘ |
| supersededBy |
Barycentric Dynamical Time
ⓘ
Geocentric Dynamical Time ⓘ
linked to:
Geocentric Coordinate Time
|
| timeUnit | ephemeris second ⓘ |
| underlyingProblemAddressed | irregular rotation of the Earth ⓘ |
| usedFor | providing a uniform measure of time ⓘ |
| usedIn |
celestial mechanics
ⓘ
high-precision astronomical observations ⓘ planetary ephemerides ⓘ |
How these facts were elicited
The pipeline generated the facts above by prompting gpt-5.1 with this entity's name + description and the instruction below.
Instruction
You are a knowledge base construction expert. Given a subject entity and a description of it, return factual statements that you know for the subject as a JSON list of dictionaries(triples), where keys must be "subject", "predicate" and "object". The number of facts may be very high, between 25 to 50 or more, for very popular subjects. For less popular subjects, the number of facts can be very low, like 5 or 10. # Requirements - If you don't know the subject at all, return an empty list. - If the subject is not a named entity, return an empty list. - Include at least one triple where predicate is "instanceOf". - Do not get too wordy. - Separate several objects into multiple triples with one object.
Input
Subject: Ephemeris Time Description of subject: Ephemeris Time is a former astronomical time standard based on the orbital motion of the Earth around the Sun, used to provide a uniform measure of time before being replaced by more precise atomic-based scales.
Referenced by (3)
Full triples — surface form annotated when it differs from this entity's canonical label.