DevLog: Phase 18 to now

P18, line shapes. Real lines are not infinitely thin spikes. Atoms move (Doppler) and get jostled by neighbours (pressure), so each line spreads into a bell shape, a Voigt profile. I added that, plus a zoom so you can look at one line up close. The useful trick was a flux-closure check: whatever area a line has before broadening, it has to still have after. That caught two grid bugs that were invisible on screen.

P19, optical depth. Until now every line acted as if light escaped freely. In a thick gas strong lines saturate, so doubling the atoms stops doubling the brightness. That is the curve of growth. Lesson: decide which regime a line sits in from the physics, not by eyeballing the slope. Also the wavelength window has to widen as the column thickens, or you clip the wings you are trying to measure.

P20, absorption. The mirror of emission. Shine a continuum through the gas, look at what is missing. The trap was that 14 hydrogen lines land on only 6 distinct wavelengths, so matching a profile to its source line by wavelength quietly pairs the wrong ones. I key on the transition instead.

P21, Hartree-Fock. The big one. Instead of a fitted screening formula, each electron feels a potential built from all the others, solved over and over until it stops changing. That gets me sulfur and chlorine, which the old model could not touch, plus ions with no preset. Two things worth remembering: the solver’s own error bar was lying to me and needed re-deriving, and what made convergence fast was not a clever algorithm, it was the right mixing constant.

P22, cleanup. Made features honest about where they apply. The classical ghost and the force-law lab only make sense for one-electron atoms, so they explain themselves now instead of erroring on a screened atom. Fixed He+ breaking every API call, because the “+” was never URL-encoded. Unknown systems say so instead of spinning. Right now I am fixing hint text that escapes its panel on narrow screens.