Qi Zheng Si Yu Coordinates and Precession: Epochs and Reference Origins

Inspect the J2000 approximation, longitude conversion and mansion anchors, with explicit astronomical limits.

View the available Qizheng calculation records

Two longitude fields

tropicalLon is the production tropical longitude. siderealLon subtracts this implementation’s accumulated precession and normalizes to 0–360°. Mansion anchor and zodiac offset default to 0° and are configurable; compare these settings before comparing placements.

Reproduce the precession arithmetic

t=(JD−2451545)/36525. Production uses p=1.396971t+0.000309t² degrees and siderealLon=normalize(tropicalLon−p). At J2000 p=0. At 2024-01-01 12:00Z, t=0.24 and p=0.3352908384°. Production solar tropical longitude 280.5518298901° becomes 280.2165390517°.

View the available Qizheng calculation records

This is not the full IAU model

Subtracting a longitude scalar does not implement the full IAU 2006/2000A precession-nutation model. Reproducible arithmetic establishes the convention, not independent ephemeris certification. SOFA is a reference for understanding the difference, not a compliance claim.

Time scales and mansion boundaries

Ephemeris JD uses clock time minus the time-zone offset. Day/hour pillars separately use local solar time; do not feed the corrected clock reading back as UT. Current mansion widths and anchors must not be equated with every historical equatorial or modern ecliptic system. Record epoch, coordinates, time scale, boundaries and offsets. Production approximates JD from UT without a separate TT/TDB or delta-T conversion; this is not a high-precision astronomical measurement claim.

What is currently available

This page provides method notes and actual engine teaching records. A personal interactive Qizheng calculator is not currently available. Expand the raw fields below to check coordinates, time scales and precession settings.

Public teaching record · 2026-10-26.1

Expand raw machine fields · 2000-01-01T12:00:00Z; longitude 0; anchor 0; zodiac offset 0

{
  "meta": {
    "ayanamsaDeg": 0,
    "epoch": "J2000",
    "xingxiuAnchorDeg": 0,
    "zodiacOffsetDeg": 0
  },
  "sun": {
    "body": "日",
    "tropicalLon": 280.3725548788095,
    "siderealLon": 280.3725548788095,
    "palace": "田宅",
    "palaceBranch": "酉",
    "xiu": "井",
    "degInXiu": 30.838308303467016,
    "dignity": "平",
    "retro": false
  }
}

Expand raw machine fields · 2024-01-01T12:00:00Z; longitude 0; anchor 0; zodiac offset 0

{
  "meta": {
    "ayanamsaDeg": 0.33529083839999996,
    "epoch": "J2000",
    "xingxiuAnchorDeg": 0,
    "zodiacOffsetDeg": 0
  },
  "sun": {
    "body": "日",
    "tropicalLon": 280.5518298900897,
    "siderealLon": 280.2165390516897,
    "palace": "田宅",
    "palaceBranch": "酉",
    "xiu": "井",
    "degInXiu": 30.682292476347214,
    "dignity": "平",
    "retro": false
  }
}

Sources and further checks

IAU SOFA: modern precession-nutation models

Maintained by the Fateverse project content team. This page explains the current calculation rules and traditional sources; it has not received an independently named professional review. Updated 27 October 2026. Compare the linked calculation records before relying on a boundary case.