One reference, and three numbers that were guessed instead
Every brightness in the scene derives from one reference. The three picked by hand were each wrong.
The simulator draws the solar system at true scale and true brightness, which puts about eleven orders of magnitude between a sunlit cloud top and a star at the limit of the naked eye. One reference holds that together. The radiance of a fully lit white surface at one astronomical unit is 1.0, and everything else is derived from it: the solar disc lands at about 46,000, a magnitude 6.5 star at two ten thousandths.
Three numbers were picked by hand instead, and all three were wrong. The first was the join between stars, which are point sources given in magnitudes, and planets, which are surfaces given in radiance. That constant was out by a factor of 4,480. The symptom was a planet that brightened all the way in and then fell off a cliff the moment it resolved into a disc.
The second was auto exposure. A luminance histogram was ruled out early, because the compute needs atomics and would not survive the fallback to WebGL2. A centre weighted log average shipped in its place, and beside a lit Earth it asked for 652 times and turned the cockpit into a white silhouette. It also fed itself, since darkening the cockpit lowered the average, which raised the exposure again. What works is the luminance weighted mean, the sum of weight times luminance squared over the sum of weight times luminance. It is linear, it needs no logarithm, a zero cannot poison it, and two accumulators and no atomics means both backends compute it identically.
The third was the Milky Way panorama, on a gain of 0.02. Once exposure was pinned to the naked eye limit rather than to taste, deep space came out as a blank white screen with the cockpit silhouetted against it, roughly three million times too bright.
A picked number is invisible in the code and glaring on the screen. Derived, the bodies check out against published magnitudes: Jupiter at opposition minus 2.77 against minus 2.7, Venus at greatest brilliancy minus 4.61 against minus 4.5, the full Moon minus 12.85 against minus 12.7.