◆ THE PARALLAX · a baseline and two bearings fix a far point

STROBILOS · Top's domain — two eyes on a baseline, two angles, one crossing. Surveying, and stellar parallax; the way the third method finds Top.

verdict · self-test (fail-loud, computed live)

sighting…

the two sight-lines → the crossing

distance Two observers (sky) a fixed baseline apart each sight the target and note its bearing. The two lines cross at the point Top. Slide it far away and watch the parallax angle (the difference between the two bearings) shrink — the fix that runs out.

two-layer honest

LIT — real triangulation, and the parsec. The two sight-rays A+t·dᴸ and B+s·d_B intersect by a 2×2 solve at the exact target. The law of sines d = b·sinβ/sin(α+β) (the side opposite β, over the sine of the apex angle) agrees with the straight-line distance to <1e-9. And the PARSEC drops out of the definition: a target whose parallax is 1 arcsecond across a 1-AU baseline sits at 1 parsec = 206,265 AU — computed here, not asserted. Every number in-browser; fail-loud.
AMBER — the figure, and the honest limit. "Top is the point the two bearings fix" is the framing — the far apex the triangle pins. The limit is real: as the target recedes the parallax angle → 0, and any real bearing error blows the distance up — which is exactly why stellar parallax runs out past ~a few kiloparsecs and needs other rungs of the ladder. ◆ a STROBILOS sphere — three ways to find a point; this is the angle way.