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.
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 NERFINISHED ⓘ |
| 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
NERFINISHED
ⓘ
Sun NERFINISHED ⓘ |
| relatedTo |
Barycentric Dynamical Time
NERFINISHED
ⓘ
Geocentric Dynamical Time NERFINISHED ⓘ International Atomic Time NERFINISHED ⓘ Terrestrial Time NERFINISHED ⓘ |
| replacedBy |
International Atomic Time
NERFINISHED
ⓘ
Terrestrial Dynamical Time NERFINISHED ⓘ Terrestrial Time NERFINISHED ⓘ atomic time scales ⓘ |
| replacedStandard | mean solar time ⓘ |
| standardizedBy | International Astronomical Union NERFINISHED ⓘ |
| status | obsolete as a primary time standard ⓘ |
| stillUsedAs | historical reference time scale ⓘ |
| supersededBy |
Barycentric Dynamical Time
NERFINISHED
ⓘ
Geocentric Dynamical Time NERFINISHED ⓘ |
| 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 ⓘ |
Referenced by (2)
Full triples — surface form annotated when it differs from this entity's canonical label.
subject surface form:
Terrestrial Time