NATARAJAStar sights to a fix — the harvest
Learning outcomes & permitted supports
- Plan a twilight round: window (Sun 6–12° down), 15–65° altitudes, ~120° azimuth spread.
- Reduce a sight at the DR: Hc and Zn from the triangle, intercept a = Ho − Hc, toward/away by 'Ho More, Toward'.
- Plot LOPs perpendicular to their azimuths, read the cocked hat honestly, and take the least-squares fix.
- Distinguish random from systematic error by what it does to the hat and the fix (1′ = 1 nm, live).
Supports in this lab: engine fix pipeline (closure ≤0.15 nm in golden suite), twilight planner, live plotting sheet with cocked hat and truth reveal, per-sight and constant error injection.
Glossary: GP · circle of equal altitude · position line · intercept · DR · cocked hat · twilight
1 · Plan the round — twilight window and star picks (engine)
Evening sight window 2026-08-17: 13:44 UT → 14:09 UT (Sun −6° to −12° — horizon AND stars, ~25 minutes)
| Round | Star | Mag | Alt | Zn |
|---|---|---|---|---|
| ★ 1 | Arcturus | -0.1 | 59° | 285° |
| ★ 2 | Altair | 0.8 | 39° | 89° |
| ★ 3 | Antares | 1.1 | 50° | 178° |
| spare | Eltanin | 2.2 | 47° | 21° |
| spare | Dubhe | 1.8 | 16° | 331° |
Picked deterministically: 15–65° high (low = refraction risk, high = azimuth uncertainty), mag ≤ 2.6, maximum azimuth spread — three cuts ~120° apart brace the fix in every direction.
2 · Shoot, reduce, plot — the fix laboratory
| Star | Hc | Zn | a |
|---|---|---|---|
| Arcturus | 058° 37.6′ | 285.0° | 7.1′ A |
| Altair | 039° 11.4′ | 89.1° | 5.9′ T |
| Antares | 050° 18.1′ | 178.0° | 5.2′ T |
FIX 13° 06.0′ N · 074° 30.0′ E
distance from true position: 0.01 nm
cocked-hat sides ≤ 0.0 nm
Perfect sights close on the truth no matter how wrong the DR is — slide the DR errors and watch the intercepts absorb them. One star's error of 2′ drags the fix ~2 nm (1′ = 1 nm, live); the SAME error on all three shifts the whole fix but barely opens the hat — the classic signature of an index or dip error.