Solar compass 太陽羅盤 true north
Sight the sun with any magnetic compass, type in the bearing you read, and get a true-north correction computed by the same astronomical kernel as our API. The sun's azimuth is astronomy, not guesswork — verified against the NOAA Solar Calculator to 0.015°. No direction is ever inferred from photos: the camera only aims.
Advanced: type coordinates 手动输入经纬度
Quick picks:
The sun right now
① set your location above → ② aim at the sun (eyes or camera — aiming only) → ③ type the bearing your compass shows, below.
Technical details 技术细节（refraction / hour angle / provenance）
Computed locally in your browser by the same WASM kernel as the /v1/sun API. Device clock is used — keep it network-synced; the sun moves 0.25° per minute.
True-north correction 真北修正
Aim at the sun (camera or naked eye — aiming only), then type the magnetic bearing you read:
实测坐向 → 24 山判定 （27 T10：误差带进结论）
用上面的修正把磁罗盘读数换成真坐向，并按误差区间判 24 山（下卦 ±4.5° / 兼向 4.5–7.5° / 跨界保留多候选）。
界线规则来自内核「下卦/替卦分界（中心 ±4.5°，兼向至 7.5°）」。区间跨线时并列候选，不替用户选。跨线=需复测或按多候选复核。
How it works
- Kernel: apparent solar longitude from VSOP87D + FK5 + nutation + aberration → declination & right ascension → Greenwich apparent sidereal time (Meeus 12.4) → local hour angle → azimuth/elevation. ΔT (TT−UT1) is applied; the Sæmundsson refraction is reported separately and flagged uncertain below 10°.
- Correction: correction = computed solar azimuth − your magnetic bearing. Add it to any magnetic reading at the same spot to get true north (positive = your compass reads east of true north). Uncertainty = √(clock term² + reading term²), clock term = 0.0042°/s × 60 s assumed device skew.
- Cross-reference: the WMM2025/IGRF-14 model declination for your location is shown for comparison; the difference between it and your measured correction is your instrument's local bias.
- Verified: frozen golden set of 58 vectors vs the NOAA GML Solar Calculator (max 0.015° azimuth / 0.004° elevation), plus sunrise/sunset cross-checks over 20 cities × 12 months — same numbers, reproducible
input_digest.
Honest boundaries
- No orientation from photos: the sitting direction of a building is never inferred from an image. The camera is a pointing aid; the numbers come from the kernel and your compass reading.
- Low sun warning: below 10° elevation the refraction depends on temperature and pressure and is flagged uncertain; below the horizon the sun cannot be used for sighting (polar day/night is reported explicitly).
- Clock skew dominates: 60 s of device clock error ≈ 0.25° of azimuth. Network-synced time assumed ±60 s in the uncertainty budget.
- Cultural and educational use only — a measurement tool, not a prediction.