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Loading contentA continuous atomic timescale kept by hundreds of atomic clocks worldwide — the stable foundation from which civil time is derived. TAI never inserts leap seconds, making it ideal for measuring precise intervals.
time_standard:taiDataset membership
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Planned API: GET /api/v0/entities/time_standard:tai
Scientific entity. See the evidence framework and authority dashboard.
How International Atomic Time (TAI) connects across Asteria Star — scientific, cultural, and astrological links are kept separate.
A miniaturised, ultra-stable atomic clock small enough to fly on a spacecraft. By putting precise timekeeping onboard, it enables one-way radiometric navigation — the spacecraft can determine its own position without the round-trip to a ground clock — a technology demonstrated in Earth orbit.
The civil time standard, derived from International Atomic Time but kept within a second of the Earth's rotation by occasional leap seconds. Deep-space tracking tags its measurements in UTC.
The continuous timescale of the Global Positioning System, offset from TAI by a fixed number of seconds and widely used to synchronise ground equipment.
The idealised time on the Earth's surface used as the time axis for astronomical events and geocentric ephemerides. It runs at the same rate as International Atomic Time but is offset ahead of it by a fixed 32.184 seconds, for continuity with the older ephemeris time.
Time kept by the real Sun, as a sundial shows it — noon is the moment the Sun crosses the meridian. Because the Earth's orbit is elliptical and tilted, the Sun runs fast or slow through the year, so clocks keep mean solar time instead, differing by up to about a quarter of an hour.
The time coordinate of the Solar System barycentre, used as the independent variable of the planetary ephemerides. It differs from Terrestrial Time only by small periodic terms arising from the Earth's motion around the Sun, never drifting by more than a couple of milliseconds.
The civil time standard, derived from International Atomic Time but kept within a second of the Earth's rotation by occasional leap seconds. Deep-space tracking tags its measurements in UTC.
The continuous timescale of the Global Positioning System, offset from TAI by a fixed number of seconds and widely used to synchronise ground equipment.
A continuous count of days (and fractions) since noon Universal Time on 1 January 4713 BC in the proleptic Julian calendar, used throughout astronomy to timestamp observations without the awkwardness of calendar months and leap years. The Modified Julian Date (MJD = JD − 2400000.5) shifts the origin to a recent midnight for convenience.
Time kept by the stars rather than the Sun — it measures the Earth's rotation relative to the fixed sky. A sidereal day is about four minutes shorter than a solar day, because the Earth must turn a little further each day to face the Sun again as it moves along its orbit.
Facts on this topic will be cited from these primary and reference sources.
Mission data, planetary science, space telescopes, and public-domain imagery.
Most NASA-produced imagery is in the public domain; individual items are checked for usage terms before publication.