Conventions registry

Look up what a receipt's ids mean.

A receipt from @zodiacs/engine or the compute API says how its numbers were found by naming conventions: the zodiac, the frame, the house system, the ΔT model and so on. A conformance vector names the quantity it tests and its arbiter the same way. This registry gives each of those names an id, a definition and its sources, and an address on this page.

An id is a namespace, a colon and a value, such as zodiac:tropical or house:placidus. The value is everything after the first colon and may itself hold semicolons, slashes or an @. A receipt that holds a value under a field names the id of that field's namespace and that value: a natal receipt whose conventions.zodiac is tropical names zodiac:tropical.

Version 2026-10-18 holds 154 ids in 57 namespaces, from @zodiacs/engine 1.0.0 (commit 7307665) and conformance suite 0.1.0. 8 of them are superseded: earlier engine versions wrote them, and the engine still reads their receipts. The registry is dedicated to the public domain under CC0 1.0, as the conformance suite is. It is also a JSON file, with each id's address, and a Markdown twin.

Calculation conventions

zodiac · Zodiac

How longitudes are counted.

Named in: natal receipts: conventions.zodiac; calc receipts: conventions.

zodiac:tropicalTropical zodiac

Longitudes counted from the equinox of the frame the position is given in. A natal receipt's positions are on the ecliptic and true equinox of date, so its zodiac counts from the true equinox of date.

Written by engine 0.1.1-rc.16 to 1.0.0; 0.1.1-rc.15; 0.1.1-rc.8 to rc.14; 0.1.1-rc.7; 0.1.1-rc.3 to rc.6.

zodiac:siderealSidereal zodiac

Longitudes counted from an ayanamsa's sidereal zero point: the longitude in the ecliptic of date less the true ayanamsa (true equinox) or the mean one (mean equinox). The receipt's ayanamsa id names which ayanamsa.

ayanamsa · Ayanamsa

The offset between the tropical and a sidereal zodiac. A built-in ayanamsa carries its own citation; a caller's ayanamsa is held in the receipt's request.

Named in: calc receipts: conventions; the engine's sidereal charts.

ayanamsa:lahiriLahiri (Chitrapaksha)

23°15′00.658″ true at 1956-03-21 0h TT, with IAU 1976 precession, held at J2000.0 and carried on by the engine's precession.

ayanamsa:fagan-bradleyFagan–Bradley

24°02′31.36″ mean at B1950.0 (JD 2433282.42345905 TT), from the synetic vernal point at 335°57′28.64″, with Newcomb's precession.

ayanamsa:krishnamurtiKrishnamurti (KP)

22°21′50″ at 1900-01-01 0h TT (JD 2415020.5), with Newcomb's precession: a fit to Krishnamurti's own table.

ayanamsa:ramanRaman

(year − 397) × 50⅓″: zero at J397.0 (JD 1866049.25 TT), growing by 50⅓″ a Julian year, as B. V. Raman gives the formula (1935).

ayanamsa:yukteswarSri Yukteswar

20°54′36″ at the March equinox of 1894 (JD 2412908.1244 TT), growing by 54″ a Julian year, as Sri Yukteswar gives it (1894).

ayanamsa:true-chitraTrue Chitra (Spica at 180°)

Spica (α Vir) at 180°: the star's apparent geocentric longitude of date, from the Hipparcos new reduction, held at that sidereal longitude.

ayanamsa:true-revatiTrue Revati (ζ Psc at 359°50′)

ζ Psc at 359°50′, held as for True Chitra.

ayanamsa:true-pushyaTrue Pushya (δ Cnc at 106°)

δ Cnc at 106°, held as for True Chitra.

ayanamsa:galactic-centerGalactic Center at 0° Sagittarius

Sgr A* at 240° (0° Sagittarius), from its ICRS radio position with Reid and Brunthaler's proper motion, treated as infinitely distant.

ayanamsa:user-epochA caller's ayanamsa at an epoch

A mean ayanamsa the caller gives at an epoch, carried by the engine's precession, or held where the Newcomb or IAU 1976 precession puts it at J2000.0 when the caller names that model. The receipt's request holds the definition.

ayanamsa:user-linearA caller's linear ayanamsa

An ayanamsa the caller gives as a value at an epoch plus a fixed rate in arcseconds per Julian year, with no precession model. The receipt's request holds the definition.

frame · Frame

The plane and equinox a position is given in. In an equatorial frame the longitude is right ascension, in degrees, and the latitude is declination.

Named in: calc receipts: conventions.

frame:ecliptic-true-of-dateEcliptic, true equinox of date

The ecliptic of date and the true equinox: IAU 2006 precession, the IAU 2006 mean obliquity and the IAU 2000B nutation in longitude. The frame of a natal chart's positions.

frame:ecliptic-mean-of-dateEcliptic, mean equinox of date

The ecliptic and mean equinox of date: the same rotation without the nutation.

frame:ecliptic-j2000Ecliptic of J2000.0

The mean ecliptic and equinox of J2000.0: the mean equator and equinox of J2000.0 turned by the IAU 2006 obliquity of J2000.0, 84381.406″.

frame:ecliptic-icrsEcliptic on ICRS axes

The ICRS turned by 84381.406″ about its x axis.

frame:equatorial-true-of-dateEquator, true equinox of date

The true equator and equinox of date: apparent right ascension and declination, with IAU 2006 precession and the IAU 2000B nutation, on the true obliquity.

frame:equatorial-mean-of-dateEquator, mean equinox of date

The mean equator and equinox of date: the precession alone.

frame:equatorial-j2000Equator of J2000.0

The mean equator and equinox of J2000.0, the axes astronomy-engine's precession starts from (EQJ).

frame:equatorial-icrsICRS

The ICRS: the J2000.0 equator less the IAU 2000 frame bias.

center · Center

The origin a position is seen from.

Named in: calc receipts: conventions.

center:geocentricGeocentric

Seen from the Earth's centre.

center:heliocentricHeliocentric

Seen from the Sun's centre.

center:barycentricBarycentric

Seen from the solar-system barycentre, as astronomy-engine finds it from the Sun and the four giant planets.

center:topocentricTopocentric

Seen from an observer on the Earth's surface, on astronomy-engine's ellipsoid and turned by the engine's Greenwich apparent sidereal time, with no polar motion.

correction · Correction

Which corrections a position carries.

Named in: calc receipts: conventions.

correction:apparentApparent

Light time and aberration: the observer is backdated with the target, which adds the observer's aberration to first order. No gravitational deflection.

correction:astrometricAstrometric

Light time only: the target when its light left, from where the observer is when it arrives.

correction:geometricGeometric

Where the target is at the instant, from where the observer is at the instant.

correction:not-applicableNot applicable

For the lunar nodes and Lilith, geocentric points of the Moon's orbit, where the three corrections give the same position.

light-time · Light time

How the light time is solved.

Named in: calc receipts: conventions.

light-time:newtonianNewtonian light time

astronomy-engine's light-time solution, iterated until successive light times agree to 10⁻⁹ day.

aberration · Aberration

How aberration is applied.

Named in: calc receipts: conventions.

aberration:backdated-observerBackdated observer

First-order aberration from backdating the observer with the target.

deflection · Deflection

Whether gravitational light deflection is applied.

Named in: calc receipts: conventions.

deflection:noneNo deflection

No gravitational deflection of light.

moon · Moon

How the Moon's position is found.

Named in: calc receipts: conventions.

moon:series-at-instantLunar series at the instant

The engine's Moon: astronomy-engine's lunar series at the instant, without light time or aberration.

precession · Precession

The precession model.

Named in: calc receipts: conventions.

precession:iau2006IAU 2006 precession

The angles of Capitaine et al. (2003) as astronomy-engine applies them, without a frame bias; named in every frame for the lunar nodes and Lilith, which are found in the ecliptic of date.

nutation · Nutation

The nutation model, in either receipt.

Named in: natal receipts: conventions.nutation; calc receipts: conventions.

nutation:iau2000bIAU 2000B

The engine's IAU 2000B nutation (McCarthy and Luzum 2003): all 77 luni-solar terms and the two fixed planetary offsets.

nutation:iau2000b;equation-of-equinoxes-with-two-complementary-termsIAU 2000B, with complementary terms

The engine's IAU 2000B series, all 77 luni-solar terms and the two fixed planetary offsets, with the two largest complementary terms in the equation of the equinoxes.

Written by engine 0.1.1-rc.16 to 1.0.0.

obliquity · Obliquity

The obliquity of the ecliptic.

Named in: calc receipts: conventions.

obliquity:iau2006IAU 2006 obliquity

The IAU 2006 mean obliquity, 84381.406″ at J2000.0, with the nutation in obliquity for a true-of-date frame; named in every frame for the lunar nodes and Lilith.

frame-bias · Frame bias

The rotation between the ICRS and the J2000.0 equator.

Named in: calc receipts: conventions.

frame-bias:iau2000IAU 2000 frame bias

The IAU 2000 frame bias of the ICRS (IERS Conventions 2010, equation 5.21).

barycentre · Barycentre

How the solar-system barycentre is found.

Named in: calc receipts: conventions.

barycentre:sun-and-giant-planetsSun and giant planets

astronomy-engine's solar-system barycentre, from the Sun and the four giant planets, each weighted m / (m + M☉).

observer · Observer

Where a topocentric observer stands.

Named in: calc receipts: conventions.

observer:iers2003-ellipsoid;no-polar-motionIERS 2003 ellipsoid, no polar motion

The topocentric observer's position and velocity on the IERS 2003 ellipsoid, without polar motion.

node · Lunar node

Which lunar node.

Named in: calc receipts: conventions.

node:true-osculatingTrue (osculating) node

The node of the Moon's osculating orbit, from its geocentric state vector.

node:meanMean node

The Moon's mean node: IERS 2003's Ω plus the nutation in longitude.

lilith · Lilith

Which Black Moon Lilith.

Named in: calc receipts: conventions.

lilith:meanMean Lilith

Black Moon Lilith as the Moon's mean apogee.

speed · Speed

How speeds are found, in either receipt.

Named in: natal receipts: conventions.speed; calc receipts: conventions.

speed:analyticAnalytic speeds

For geometric positions on fixed axes (the J2000.0 and ICRS frames) of every body but the Moon: astronomy-engine's velocities from its differentiated series (Pluto's from its integrator), turned into the frame.

speed:central-difference-0.001dCentral difference, ±0.001 day

The value at t + h less the value at t − h, over 2h, with h = 0.001 day: the method wherever speeds are not analytic.

speed:central-difference-0.25dCentral difference, ±0.25 day

Central difference with h = 0.25 day, for the true node, whose short-period motion would otherwise dominate.

speed:degrees-per-day;central-difference-plus-minus-0.001-day;nodes-plus-minus-0.25-dayDegrees per day, ±0.001 day, nodes ±0.25 day

Speeds in degrees per day by central difference over ±0.001 day, and over ±0.25 day for the nodes.

Written by engine 0.1.1-rc.16 to 1.0.0; 0.1.1-rc.15; 0.1.1-rc.8 to rc.14; 0.1.1-rc.7.

speed:degrees-per-day;central-difference-plus-minus-0.25-dayDegrees per day, ±0.25 daysuperseded

Speeds in degrees per day by central difference over ±0.25 day.

Written by engine 0.1.1-rc.3 to rc.6.

ephemeris · Ephemeris

The ephemeris, by name and version. A natal receipt names it in engine.ephemeris.

Named in: calc receipts: conventions; natal receipts: engine.ephemeris (name@version).

ephemeris:astronomy-engine@2.1.19astronomy-engine 2.1.19

astronomy-engine 2.1.19: truncated VSOP87 for the planets, a lunar series after Brown's theory as Montenbruck and Pfleger give it, and an integrated Pluto.

deltat · ΔT source

Where a calc receipt's ΔT comes from. Not the natal receipt's deltaT convention, which is its own namespace.

Named in: calc receipts: conventions.

deltat:time-basisΔT from the time basis

ΔT from the engine's time basis: iers-utc/1 from 1972-01-01 to the end of the IERS table, zodiacs-deltat/1 outside it; each instant's deltaT.model says which.

deltat:pinnedPinned ΔT

The caller's ΔT value, pinned.

time · Time basis

How a calc receipt's instants become UT1 and TT.

Named in: calc receipts: conventions.

time:tt-from-leap-seconds-and-ut1-from-iers-1972-to-table-end;delta-t-model-otherwiseThe engine's time basis

From 1972-01-01 to the end of the IERS UT1 table, TT from the leap seconds (UTC + (TAI − UTC) + 32.184 s) and UT1 from IERS UT1 − UTC; outside that span, the instant read as UT1 and TT from the ΔT model. The natal receipt names the same basis in its timeScale convention.

house · House system

The house system. A natal receipt names the system asked for and the one used in houses.requested and houses.actual; the compute API takes the same names.

Named in: calc receipts: conventions; natal receipts: houses.requested, houses.actual; compute API requests: houseSystem.

house:wholeWhole sign

Each sign is a house, the first the ascendant's.

house:placidusPlacidus

The semi-arcs of each degree divided in thirds. Undefined where |latitude| ≥ 90° − ε.

house:porphyryPorphyry

Each quadrant between the angles divided into three equal arcs of longitude.

house:equalEqual

30° each from the ascendant.

house:equal-mcEqual from the midheaven

30° each, the 10th from the midheaven; the same at every latitude.

house:vehlowVehlow

30° each, with the ascendant in the middle of the first.

house:kochKoch

Ascendants at thirds of the midheaven degree's semi-arc. Undefined where |latitude| ≥ 90° − ε.

house:regiomontanusRegiomontanus

Circles through the horizon's north and south points, every 30° of the equator.

house:campanusCampanus

Circles through the horizon's north and south points, every 30° of the prime vertical.

house:topocentricTopocentric (Polich–Page)

Regiomontanus's ascensions, with pole heights at one and two thirds of the latitude's tangent.

house:alcabitiusAlcabitius

The ascendant's semi-arcs divided in thirds on the equator, along hour circles.

house:morinusMorinus

The equator every 30° from the midheaven's right ascension, carried to the ecliptic through its poles.

house:meridianMeridian (axial rotation)

Right ascensions every 30° from the midheaven's; the 1st cusp is the equatorial ascendant.

polar-fallback · Polar fallback

What the engine uses where a house system is undefined.

Named in: calc receipts: conventions.

polar-fallback:wholeWhole sign in polar regions

Whole-sign houses where Placidus or Koch is undefined, at |latitude| ≥ 90° − ε with ε the true obliquity of date; the chart also carries the polar-fallback flag.

angles · Angles

How the ascendant and midheaven are found.

Named in: natal receipts: conventions.angles; calc receipts: conventions.

angles:gast-and-true-obliquityApparent sidereal time and true obliquity

The angles from the engine's Greenwich apparent sidereal time and the true obliquity of date.

Written by engine 0.1.1-rc.16 to 1.0.0; 0.1.1-rc.15; 0.1.1-rc.8 to rc.14; 0.1.1-rc.7.

angles:gast-and-mean-obliquityApparent sidereal time and mean obliquitysuperseded

The angles from Greenwich apparent sidereal time and the mean obliquity of date.

Written by engine 0.1.1-rc.3 to rc.6.

sidereal-time · Sidereal time

How Greenwich apparent sidereal time is found.

Named in: calc receipts: conventions.

sidereal-time:gast-iau2006-eraGAST from the Earth rotation angle

Greenwich apparent sidereal time from the Earth rotation angle, astronomy-engine's IAU 2006 polynomial, and the equation of the equinoxes: Δψ cos εA and the two largest IAU 2000 complementary terms.

aspects · Aspects

Which aspects a chart lists and how.

Named in: natal receipts: conventions.aspects; calc receipts: conventions.

aspects:majorMajor aspects

The chart's major aspects, as a calc chart lists them.

aspects:major-aspects;sun-moon-eight-planets;no-nodes;applying-instantaneous-orb-rateMajor aspects, applying by orb rate

The major aspects among the Sun, the Moon and the eight planets, not the nodes, each applying or separating by the instantaneous rate of change of its orb.

Written by engine 0.1.1-rc.16 to 1.0.0; 0.1.1-rc.15; 0.1.1-rc.8 to rc.14; 0.1.1-rc.7.

aspects:major-aspects;sun-moon-eight-planets;no-nodesMajor aspectssuperseded

The major aspects among the Sun, the Moon and the eight planets, not the nodes.

Written by engine 0.1.1-rc.3 to rc.6.

Natal receipt conventions

calendar · Calendar

The calendar dates are written in.

Named in: natal receipts: conventions.calendar.

calendar:proleptic-gregorianProleptic Gregorian

Dates in the Gregorian calendar, extended before its adoption in 1582.

Written by engine 0.1.1-rc.16 to 1.0.0; 0.1.1-rc.15; 0.1.1-rc.8 to rc.14; 0.1.1-rc.7; 0.1.1-rc.3 to rc.6.

deltaT · ΔT

What a natal receipt's ΔT is and where it is given. Not the calc receipt's deltat source.

Named in: natal receipts: conventions.deltaT.

deltaT:tt-minus-ut1;value-in-resultTT − UT1, in the result

ΔT is TT − UT1, and the result gives its value; the time basis decides how the instant is read.

Written by engine 0.1.1-rc.16 to 1.0.0; 0.1.1-rc.15.

deltaT:tt-minus-ut1;ut1-read-as-utc;value-in-resultTT − UT1, the instant read as UT1superseded

ΔT is TT − UT1, the instant is read as UT1, and the result gives the value.

Written by engine 0.1.1-rc.8 to rc.14.

localTime · Local time

How a local wall time becomes UTC.

Named in: natal receipts: conventions.localTime.

localTime:tzdb-shards-before-1970;host-intl-from-1970;flags-from-transition-recordShipped tzdb before 1970, Intl from 1970

Local times before 1970 resolved on the tzdb history the engine ships, from 1970 on the host's Intl, and the gap, fold and local-mean-time flags taken from the transition record.

Written by engine 0.1.1-rc.16 to 1.0.0; 0.1.1-rc.15.

longitudeUnit · Longitude unit

The unit and range of longitudes.

Named in: natal receipts: conventions.longitudeUnit.

longitudeUnit:degrees-[0,360)Degrees in [0, 360)

Longitudes in degrees, from 0 up to but not including 360.

Written by engine 0.1.1-rc.16 to 1.0.0; 0.1.1-rc.15; 0.1.1-rc.8 to rc.14; 0.1.1-rc.7; 0.1.1-rc.3 to rc.6.

moonNodes · Moon nodes

Which lunar nodes a natal chart gives.

Named in: natal receipts: conventions.moonNodes.

moonNodes:instantaneous-geocentric-moon-orbit-planeInstantaneous orbit plane

The nodes of the plane of the Moon's instantaneous geocentric orbit: the true (osculating) nodes.

Written by engine 0.1.1-rc.16 to 1.0.0; 0.1.1-rc.15; 0.1.1-rc.8 to rc.14; 0.1.1-rc.7; 0.1.1-rc.3 to rc.6.

moonPosition · Moon position

How a natal chart's Moon is found.

Named in: natal receipts: conventions.moonPosition.

moonPosition:astronomy-engine-geo-moon;no-light-time;no-aberrationastronomy-engine GeoMoon, ecliptic of date

astronomy-engine's geocentric lunar series (GeoMoon), turned to the ecliptic of date by the engine's precession and nutation, without light time or aberration.

Written by engine 0.1.1-rc.16 to 1.0.0.

moonPosition:astronomy-engine-ecliptic-geo-moon;no-light-time;no-aberrationastronomy-engine EclipticGeoMoon, uncorrectedsuperseded

astronomy-engine's ecliptic geocentric Moon (EclipticGeoMoon), without light time or aberration.

Written by engine 0.1.1-rc.15; 0.1.1-rc.8 to rc.14.

moonPosition:astronomy-engine-ecliptic-geo-moonastronomy-engine EclipticGeoMoonsuperseded

astronomy-engine's ecliptic geocentric Moon (EclipticGeoMoon).

Written by engine 0.1.1-rc.7; 0.1.1-rc.3 to rc.6.

planetPositions · Planet positions

How a natal chart's planets are found.

Named in: natal receipts: conventions.planetPositions.

planetPositions:aberrated-geocentric-ecliptic-of-date;no-deflectionGeocentric, light time and aberration, ecliptic of date

Geocentric positions corrected for light time and aberration but not for gravitational deflection, on the ecliptic of date.

Written by engine 0.1.1-rc.16 to 1.0.0; 0.1.1-rc.15; 0.1.1-rc.8 to rc.14.

planetPositions:apparent-geocentric-ecliptic-of-dateApparent geocentric, ecliptic of datesuperseded

Apparent geocentric positions on the ecliptic of date.

Written by engine 0.1.1-rc.7; 0.1.1-rc.3 to rc.6.

timeScale · Time scale

How a natal chart's instant becomes UT1 and TT, and where the basis is recorded.

Named in: natal receipts: conventions.timeScale.

timeScale:tt-from-leap-seconds-and-ut1-from-iers-1972-to-table-end;delta-t-model-otherwise;in-resultThe engine's time basis, in the result

From 1972-01-01 to the end of the IERS UT1 table, TT from the leap seconds and UT1 from IERS UT1 − UTC; otherwise the instant read as UT1 and TT from the ΔT model; the basis recorded in the result's timeScale.

Written by engine 0.1.1-rc.16 to 1.0.0; 0.1.1-rc.15.

Natal receipt fields and time records

house-absence · House absence

Why a natal chart has no houses.

Named in: natal receipts: houses.absenceReason.

house-absence:unknown-timeUnknown birth time

The birth time is unknown, so the chart has no angles or houses.

house-absence:missing-locationNo birthplace

No birthplace was given, so the chart has no angles or houses.

flag · Chart flag

A condition a natal chart reports, in the receipt's input and result flags.

Named in: natal receipts: inputFlags, resultFlags; compute API answers: flags.

flag:dst-gapClock gap

The local time fell in a gap of any cause, such as a change to summer time, and was moved forward.

flag:dst-foldClock fold

The local time fell in a fold of any cause and could be read twice; the earlier reading was taken.

flag:lmtLocal mean time

A local mean time clock read the wall time.

flag:no-timeNo birth time

The birth time is unknown; the chart has no angles or houses.

flag:polar-fallbackPolar fallback

Placidus or Koch was asked for where it is undefined, and the chart uses whole-sign houses.

flag:outside-reference-spanOutside the reference span

The instant lies outside 1800-01-01 to 2200-01-01, the span over which positions were compared with an independent ephemeris (the engine's REFERENCE_SPAN); the chart is still computed.

reference · Reference instant

Which instant a natal chart is cast for.

Named in: natal receipts: reference.

reference:supplied-instantThe supplied instant

The chart is cast for the instant given.

reference:utc-noonNoon UTC

An untimed chart cast for 12:00 UTC on the date.

reference:local-noonLocal noon

An untimed chart cast for 12:00 local time on the date.

time-scale · Instant time scale

The scale of a receipt's instant.

Named in: natal receipts: timeScale; calc receipts: instants[].timeScale.input.

time-scale:utcUTC

Coordinated Universal Time.

time-scale:ut1UT1

Universal Time, the Earth's rotation angle as a time.

time-scale:ttTT

Terrestrial Time: TAI + 32.184 s.

time-basis · Time basis

Which branch of the time basis an instant took.

Named in: calc receipts: instants[].timeScale.basis; natal results: timeScale.basis.

time-basis:iersIERS

From 1972-01-01 to the end of the IERS table: TT from the leap seconds, UT1 from IERS UT1 − UTC.

time-basis:delta-tΔT model

Outside the IERS span: the instant read as UT1, TT from the ΔT model.

time-basis:pinnedPinned

The caller pinned ΔT: TT is UT1 plus the pin.

deltat-model · ΔT model

Which source gave an instant's ΔT.

Named in: calc receipts: instants[].deltaT.model; natal results: deltaT.model; compute API receipts: deltaT[].model.

deltat-model:iers-utc/1IERS, through UTC

ΔT = 32.184 s + (TAI − UTC) − (UT1 − UTC), from the IERS leap seconds and UT1 table.

deltat-model:zodiacs-deltat/1The engine's ΔT model

The reconstruction of Stephenson, Morrison and Hohenkerk (2016) up to 1941, observed USNO and IERS values after that, then Bulletin A's predictions and a damped extrapolation, with a 1-σ band.

deltat-model:pinnedPinned

The caller's pinned value, with no band or table.

deltat-segment · ΔT segment

Which part of its source an instant's ΔT came from.

Named in: calc receipts: instants[].deltaT.segment; natal results: deltaT.segment.

deltat-segment:long-termLong-term

Before the year −720: the integral of Stephenson, Morrison and Hohenkerk's long-term formula for the length of day (their equation 5.1), joined in value at −720.

deltat-segment:reconstructedReconstructed

From −720 to 1956: Stephenson, Morrison and Hohenkerk's Table S15 as a cubic spline to 1941, then whole-year knots from USNO's historic ΔT.

deltat-segment:observedObserved

In the model, from 1956 to the last observed day: USNO, IERS 20 C04 and IERS finals2000A's observed rows. On the IERS basis, a ΔT whose UT1 − UTC is observed.

deltat-segment:predictedPredicted

In the model, to the last predicted day: knots from Bulletin A's predictions. On the IERS basis, a ΔT whose UT1 − UTC is predicted.

deltat-segment:extrapolatedExtrapolated

After the last predicted day: the prediction window's slope, damped with a 15-year time constant, plus the curvature of the long-term curve.

deltat-segment:pinnedPinned

The caller's pinned value of ΔT.

deltat-segment:fallbackFallbacksuperseded

The IERS basis with UT1 − UTC taken as 0 ± 0.9 s past the table's ends. Only 0.1.1-rc.15's first cut wrote it; later releases read it so those records stay readable.

Written by engine 0.1.1-rc.15 (its first cut).

ut1-source · UT1 − UTC source

Where an instant's UT1 − UTC came from.

Named in: calc receipts: instants[].timeScale.ut1MinusUtc.source; natal results: timeScale.ut1MinusUtc.source.

ut1-source:observedObserved

UT1 − UTC from an observed row of the IERS table.

ut1-source:predictedPredicted

UT1 − UTC from a predicted row of the IERS table.

ut1-source:fallbackFallback

After the table, for UTC or TT input: 0 ± 0.9 s.

Coverage statements

assessment · Coverage: assessment

What a receipt's numbers were checked against, from its coverage statements.

Named in: natal receipts: coverage.assessment; compute API receipts: coverage.assessment.

assessment:finite-reference-cases-onlyFinite reference cases only

The numbers were checked against a finite set of reference cases only.

broadDateRange · Coverage: broad date range

Whether the numbers are certified across a broad range of dates.

Named in: natal receipts: coverage.broadDateRange; compute API receipts: coverage.broadDateRange.

broadDateRange:not-certifiedNot certified

The numbers are not certified across a broad range of dates.

angleExclusions · Coverage: angle exclusions

Where the angles are not covered.

Named in: natal receipts: coverage.angleExclusions; compute API receipts: coverage.angleExclusions.

angleExclusions:exact-geographic-poles-and-ecliptic-horizon-coincidenceThe poles and an ecliptic on the horizon

The angles are not covered at the exact geographic poles or where the ecliptic coincides with the horizon.

inputSyntax · Coverage: input syntax

What accepting an input means.

Named in: natal receipts: coverage.inputSyntax; compute API receipts: coverage.inputSyntax.

inputSyntax:not-an-astronomical-accuracy-guaranteeNot an accuracy guarantee

That an input is accepted guarantees nothing about the astronomical accuracy of the answer.

Compute API receipts

endpoint · Compute endpoint

The compute API endpoint a compute receipt is for, under https://zodiacs.org/api/v1/. The chart and houses endpoints answer with the engine's own natal receipt, which names no endpoint.

Named in: compute API receipts: endpoint.

endpoint:positionsPositions

Positions of the bodies at one or more instants.

endpoint:eventsEvents

The ingresses, stations and lunations in a window.

endpoint:timeTime

A local time resolved to UTC and Terrestrial Time.

endpoint:sky-factSky fact

Whether a stated sky fact holds, answered true, false or depends.

endpoint:electionsElections

The stretches of a window in which every stated condition holds.

search-solver · Search solver

The solver a compute search used.

Named in: compute API receipts: search.solver, electionSearch.solver.

search-solver:engine-longitude-crossingsThe engine's longitude crossings

The engine's one crossing solver, with its scan steps and 24 bisections a crossing.

search-solver:engine-longitude-crossings-and-sampled-housesLongitude crossings and sampled houses

The crossing solver for sign changes, stations and phases, with the houses sampled at a fixed step for angular conditions.

search-window · Search window

Which ends of a compute search's window count.

Named in: compute API receipts: search.window, electionSearch.window.

search-window:start-exclusive-end-inclusiveStart exclusive, end inclusive

An event exactly at the window's start is not counted; one exactly at its end is.

search-window:start-inclusive-end-exclusiveStart inclusive, end exclusive

The window includes its start and excludes its end.

completeness · Completeness

What a compute search claims about missing nothing.

Named in: compute API receipts: search.completeness, electionSearch.completeness.

completeness:tested-not-provenTested, not proven

The search's completeness is tested, not proven: it is not shown that no event between its samples was missed.

fold-policy · Fold policy

Which reading of a local time in a fold the compute API takes.

Named in: compute API receipts: timeResolution.policy.fold.

fold-policy:earlierEarlier

A local time that occurs twice is read as the earlier of the two instants.

gap-policy · Gap policy

How the compute API reads a local time in a gap.

Named in: compute API receipts: timeResolution.policy.gap.

gap-policy:shift-forwardShift forward

A local time skipped by a clock change is moved forward by the gap.

void-of-course · Void of course

The void-of-course rule an election search used.

Named in: compute API receipts: electionSearch.voidOfCourse.convention.

void-of-course:last-exact-ptolemaic-aspect-to-sign-exitLast exact Ptolemaic aspect to sign exit

The Moon is void of course from its last exact Ptolemaic aspect in a sign until it leaves the sign.

void-of-course-bodies · Void-of-course bodies

Which bodies count for the void-of-course rule.

Named in: compute API receipts: electionSearch.voidOfCourse.bodies.

void-of-course-bodies:modernModern

The bodies whose aspects with the Moon count: the Sun, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.

Conformance vectors

kind · Conformance vector kind

The quantity a conformance vector tests, as its kind field names it.

Named in: conformance vectors: kind.

kind:position.apparent.ecliptic-true-of-dateApparent positions, ecliptic of date

L1 (Positions): 240 vectors, tolerance lon ±1″ (on the circle); lat ±1″.

kind:angles.asc-mcAscendant and midheaven

L2 (Houses and angles): 60 vectors, tolerance asc ±1″ (on the circle); mc ±1″ (on the circle).

kind:angles.vertex-east-pointVertex and east point

L2 (Houses and angles): 10 vectors, tolerance vertex ±1″ (on the circle); east_point ±1″ (on the circle).

kind:houses.cuspsHouse cusps, thirteen systems

L2 (Houses and angles): 80 vectors, tolerance cusps each ±1″ (on the circle), or status exact.

kind:time.zone-offsetTime zone offsets

L3 (Time and calendars): 45 vectors, tolerance status exact; utc_offset_s exact, or status exact, or status exact; utc_offsets_s exact.

kind:time.local-mean-timeLocal mean time

L3 (Time and calendars): 5 vectors, tolerance utc_offset_s ±0.001 s.

kind:time.tt-minus-utcTT − UTC

L3 (Time and calendars): 10 vectors, tolerance tt_minus_utc_s ±0.0005 s.

kind:time.delta-tΔT (TT − UT1)

L3 (Time and calendars): 15 vectors, tolerance delta_t_s ±0.1 s.

kind:calendar.to-jdnCalendar date to day number

L3 (Time and calendars): 25 vectors, tolerance jdn exact.

kind:calendar.from-jdnDay number to calendar date

L3 (Time and calendars): 10 vectors, tolerance year exact; month exact; day exact.

arbiter · Conformance arbiter

The independent computation that gives a conformance vector its expected value, as its arbiter field names it.

Named in: conformance vectors: arbiter.

arbiter:horizons-de441-iau2006NASA JPL Horizons (DE441) apparent geocentric ecliptic positions, carried into the IAU 2006/2000A true ecliptic and equinox of date

The independent arbiter of L1 (Positions) vectors. Source: NASA JPL Horizons API 1.2 (https://ssd.jpl.nasa.gov/api/horizons.api), fetched 2026-09-22: ephemeris DE441 for every target, with Mars to Pluto as their system barycentres (NAIF 4 to 9); EOP file eop.260922.p261219 (data 1962-01-20 to 2026-09-22, predictions to 2026-12-18). One request per target: EPHEM_TYPE OBSERVER, CENTER 500@399 (the geocentre), QUANTITIES 31 (observer ecliptic longitude and latitude of date of the apparent position: light-time, gravitational deflection by the Sun, stellar aberration), APPARENT AIRLESS, TIME_TYPE TT, TLIST_TYPE JD with the 24 jd_tt values to 8 decimals, ANG_FORMAT DEG, EXTRA_PREC YES, CSV_FORMAT YES. The responses are kept verbatim in sources/horizons-24/, byte for byte as committed in the zodiacs.org site repository (ZodiacsOfficial/site, docs/platform/evidence/engine-beyond-swiss/corpora/horizons-24/, commit 3f31ba17), together with Horizons's body-centre files for Mars to Pluto (NAIF 499 to 999, from the satellite solutions mar099, jup365_merged, sat441l, ura184_merged, nep098_merged, plu060_merged), fetched the same way and used only for the body-centre measurement in the uncertainty. Plus the frame conversion: Horizons labels this frame IAU76/80 ecliptic-of-date, and the eopJpl model of it, with its per-instant celestial-pole offsets, is the horizons-frame study in the same repository (docs/platform/evidence/engine-beyond-swiss/horizons-frame/: decompose.py, results.json), the offsets copied into sources/horizons-24/frame-offsets.json.

arbiter:l2-angles-erfaERFA sidereal time and obliquity; spherical geometry of the angles

The independent arbiter of L2 (Houses and angles) vectors. Source: ERFA 2.0.1 through pyerfa 2.0.1.5 (github.com/liberfa/erfa, derived from IAU SOFA): gst06a, obl06, nut06a. UT1−UTC: IERS finals2000A (the IERS Rapid Service/Prediction Centre finals.all fetched 2026-09-22, sha256 c672540e026d3cd4840c0858d4ce2bc4a18c3bc9751f9636c3285e11950d58a1; the three columns used are the committed CSV). TAI−UTC: IERS Bulletin C, hpiers.obspm.fr/iers/bul/bulc/Leap_Second.dat (through Bulletin C 72, fetched 2026-09-28). ΔT outside the IERS span: F. Espenak and J. Meeus, Five Millennium Canon of Solar Eclipses: −1999 to +3000, NASA/TP-2006-214141 (2006). Definitions: R. W. Holden, The Elements of House Division (1977); M. P. Munkasey, An Astrological House Formulary; W. M. Smart, Textbook on Spherical Astronomy.

arbiter:l2-houses-eclipticEcliptic divisions: equal, whole-sign, Vehlow, equal-MC, Porphyry

The independent arbiter of L2 (Houses and angles) vectors. Source: ERFA 2.0.1 through pyerfa 2.0.1.5 (github.com/liberfa/erfa, derived from IAU SOFA): gst06a, obl06, nut06a. UT1−UTC: IERS finals2000A (the IERS Rapid Service/Prediction Centre finals.all fetched 2026-09-22, sha256 c672540e026d3cd4840c0858d4ce2bc4a18c3bc9751f9636c3285e11950d58a1; the three columns used are the committed CSV). TAI−UTC: IERS Bulletin C, hpiers.obspm.fr/iers/bul/bulc/Leap_Second.dat (through Bulletin C 72, fetched 2026-09-28). ΔT outside the IERS span: F. Espenak and J. Meeus, Five Millennium Canon of Solar Eclipses: −1999 to +3000, NASA/TP-2006-214141 (2006). Definitions: R. W. Holden, The Elements of House Division (1977); M. P. Munkasey, An Astrological House Formulary; W. M. Smart, Textbook on Spherical Astronomy.

arbiter:l2-houses-great-circleFixed house circles: Regiomontanus, Campanus, meridian, Morinus

The independent arbiter of L2 (Houses and angles) vectors. Source: ERFA 2.0.1 through pyerfa 2.0.1.5 (github.com/liberfa/erfa, derived from IAU SOFA): gst06a, obl06, nut06a. UT1−UTC: IERS finals2000A (the IERS Rapid Service/Prediction Centre finals.all fetched 2026-09-22, sha256 c672540e026d3cd4840c0858d4ce2bc4a18c3bc9751f9636c3285e11950d58a1; the three columns used are the committed CSV). TAI−UTC: IERS Bulletin C, hpiers.obspm.fr/iers/bul/bulc/Leap_Second.dat (through Bulletin C 72, fetched 2026-09-28). ΔT outside the IERS span: F. Espenak and J. Meeus, Five Millennium Canon of Solar Eclipses: −1999 to +3000, NASA/TP-2006-214141 (2006). Definitions: R. W. Holden, The Elements of House Division (1977); M. P. Munkasey, An Astrological House Formulary; W. M. Smart, Textbook on Spherical Astronomy.

arbiter:l2-houses-semi-arcSemi-arc and pole systems: Placidus, Koch, Alcabitius, topocentric

The independent arbiter of L2 (Houses and angles) vectors. Source: ERFA 2.0.1 through pyerfa 2.0.1.5 (github.com/liberfa/erfa, derived from IAU SOFA): gst06a, obl06, nut06a. UT1−UTC: IERS finals2000A (the IERS Rapid Service/Prediction Centre finals.all fetched 2026-09-22, sha256 c672540e026d3cd4840c0858d4ce2bc4a18c3bc9751f9636c3285e11950d58a1; the three columns used are the committed CSV). TAI−UTC: IERS Bulletin C, hpiers.obspm.fr/iers/bul/bulc/Leap_Second.dat (through Bulletin C 72, fetched 2026-09-28). ΔT outside the IERS span: F. Espenak and J. Meeus, Five Millennium Canon of Solar Eclipses: −1999 to +3000, NASA/TP-2006-214141 (2006). Definitions: R. W. Holden, The Elements of House Division (1977); M. P. Munkasey, An Astrological House Formulary; W. M. Smart, Textbook on Spherical Astronomy. Topocentric: W. Polich and A. P. Nelson Page, the topocentric system (tan of the house pole = n/3 · tan φ).

arbiter:l2-houses-undefinedCusps that do not exist: the construction has no solution in zodiacal order

The independent arbiter of L2 (Houses and angles) vectors. Source: Constructions: Placidus de Titis, Tabulae primi mobilis (Milan, 1657; English translation by J. Cooper, Primum Mobile, 1814); W. A. Koch and E. Schaeck, Häusertabellen des Geburtsortes (Göppingen, 1962); both restated in R. W. Holden, The Elements of House Division (L. N. Fowler, Romford, 1977; page numbers not verified for this file). TT, RAMC and ε as in l2-angles-erfa: ERFA 2.0.1 through pyerfa 2.0.1.5 (github.com/liberfa/erfa, derived from IAU SOFA): gst06a, obl06, nut06a. UT1−UTC: IERS finals2000A (the IERS Rapid Service/Prediction Centre finals.all fetched 2026-09-22, sha256 c672540e026d3cd4840c0858d4ce2bc4a18c3bc9751f9636c3285e11950d58a1; the three columns used are the committed CSV). TAI−UTC: IERS Bulletin C, hpiers.obspm.fr/iers/bul/bulc/Leap_Second.dat (through Bulletin C 72, fetched 2026-09-28). ΔT outside the IERS span: F. Espenak and J. Meeus, Five Millennium Canon of Solar Eclipses: −1999 to +3000, NASA/TP-2006-214141 (2006).

arbiter:tzdb-2025c-backzoneIANA tzdb 2025c with backzone, compiled by zic 2025c

The independent arbiter of L3 (Time and calendars) vectors. Source: IANA time zone database release 2025c: https://data.iana.org/time-zones/releases/tzdata2025c.tar.gz (sha256 4aa79e4effee53fc4029ffe5f6ebe97937282ebcdf386d5d2da91ce84142f957) and https://data.iana.org/time-zones/releases/tzcode2025c.tar.gz (sha256 697ebe6625444aef5080f58e49d03424bbb52e08bf483d3ddb5acf10cbd15740), both OpenPGP-signed by Paul Eggert (key 7E37 92A9 D8AC F7D6 33BC 1588 ED97 E90E 62AA 7E34; signatures checked 2026-09-28). The data are the Makefile's `make PACKRATDATA=backzone PACKRATLIST=zone.tab` build: backzone's pre-1970 history for the zone.tab zones that the main data merge into links. Why backzone: a birth chart needs the local time in force where and when the birth happened, often before 1970, and tzdb's default build does not keep that history for these zones; it makes each of them a link to another zone whose clocks have agreed with it since 1970, so the zone answers with the other zone's history (Africa/Banjul at 1880-12-31T12:00:00 gets Abidjan's local mean time, -968 s, instead of its own, -3996 s). The maintainers' caveat applies: the Makefile of tzdata 2025c offers backzone as 'out-of-scope and often-wrong data', and its theory.html says the file 'is less reliable and does not necessarily follow database guidelines'. zic and zdump are built from the same release's tzcode.

arbiter:lmt-definitionLocal mean time from longitude

The independent arbiter of L3 (Time and calendars) vectors. Source: The definition of local mean time: mean solar time at east longitude lon runs ahead of UT by lon/15 hours, 240 s of UTC offset per degree.

arbiter:iers-leap-seconds-2025cIERS leap-second table (leap-seconds.list, tzdata 2025c)

The independent arbiter of L3 (Time and calendars) vectors. Source: leap-seconds.list as distributed in tzdata 2025c (IERS Earth Orientation Centre, Paris Observatory; updated through IERS Bulletin C; last update 2025-07-07 (NTP 3960835200); expires 2026-06-28 (NTP 3991593600); its #h line, SHA-1 49db2447571e5e1b2f002a539c8da8e439b8e49e, verified). TT = TAI + 32.184 s exactly (IAU 1991 Resolution A4), so TT - UTC = 32.184 s + (TAI - UTC).

arbiter:iers-ut1-finals2000aIERS UT1 - UTC (finals2000A, observed rows) with the leap-second table

The independent arbiter of L3 (Time and calendars) vectors. Source: UT1 - UTC per day at 0h UTC from the IERS finals.all (IAU 2000) file fetched 2026-09-22 (sha256 c672540e026d3cd4840c0858d4ce2bc4a18c3bc9751f9636c3285e11950d58a1, 3,767,520 bytes), extracted to CSV (MJD, date, I/P flag, UT1 - UTC, formal error) and copied here unchanged; TAI - UTC from leap-seconds.list of tzdata 2025c (arbiter iers-leap-seconds-2025c).

arbiter:calendar-arithmeticJulian and Gregorian calendar arithmetic, two published algorithms

The independent arbiter of L3 (Time and calendars) vectors. Source: Richards, E. G. (2013), 'Calendars', in Urban & Seidelmann (eds.), Explanatory Supplement to the Astronomical Almanac, 3rd ed., sec. 15.11 (Algorithms 3 and 4, Julian and Gregorian parameters); Fliegel, H. F. & Van Flandern, T. C. (1968), Communications of the ACM 11(10), 657; Meeus, J. (1998), Astronomical Algorithms, 2nd ed., ch. 7. Both calendars proleptic, astronomical year numbering; the JDN of a civil day is the Julian date at its noon.