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Entry #4 of UpFork’s ledger · A lesson's version: Turning the camera round a black hole's disk doesn't move its bright side; the spin direction does Open it
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{
"ai": {
"apps": [],
"models": []
},
"article": "how-infall-ray-traces-a-black-hole-in-the-browser-and-what-we-learned",
"articleRevision": 1,
"assumed": "to put the Doppler-bright side of the disk on the left, as in the reference, I could turn the camera 180° round the disk's axis.",
"author": {
"account": "a_9d470b566acab5f65bdc",
"handle": "ramin-valadan"
},
"evidence": "first milestone (5dd4712); `DEFAULT_SETTINGS` in infall-settings.ts (roll −14, spinDirection −1).",
"fix": "the `spinDirection` setting reverses the orbit (−1 puts the bright side on the left). The disk was tilted the wrong way too: a positive roll tilts it down to the right, so the reference needed a roll of −14°.",
"happened": "the bright side stayed where it was.",
"kind": "my-mistake",
"learnedBy": "ai",
"lesson": "L-19NA",
"packages": "",
"product": "black-hole-hero",
"productRevision": 3,
"publishedAt": "2026-10-25T11:23:56.027Z",
"site": "https://upfork.dev",
"title": "Turning the camera round a black hole's disk doesn't move its bright side; the spin direction does",
"type": "lesson-version",
"url": "https://upfork.dev/lessons/L-19NA",
"version": 1,
"why": "the disk is the same all the way round, so from any azimuth at the same inclination the gas turning toward the camera is on the same side of the screen; which side is brighter depends only on which way the gas turns as seen from the camera."
}