Alien-scapes

Procedurally generated landscapes under other suns, where every colour on screen is computed from a spectrum rather than chosen by hand.

Pick a star, an exoplanet and an atmosphere, and the page works out what the sky, the ground, the water and — if anything can live there — the vegetation would actually look like. Then it shows you the spectra behind that answer and lets you export the whole thing as a data sheet.

→ Open Alien-scapes

No build step, no dependencies, no network calls. It is a handful of ES modules and a canvas.

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What it does

• 14 stellar presets on a spectral-class grid (O–M, dwarfs and giants) plus 28 more named stars including Wolf-Rayet, white dwarf and brown dwarf classes — and a free temperature slider from 1,000 K to 50,000 K.
• 15 exoplanet presets — Earth, Mars, Venus and Titan as controls, then TRAPPIST-1 e, Proxima b, Kepler-186 f, LHS 1140 b, TOI-700 d, K2-18 b, Kepler-452 b, GJ 667 C c, GJ 1214 b, Gliese 581 g, and the circumbinary Kepler-16 (AB) b, which really does have two suns in the sky.
• 10 atmospheres, from airless through Earth Rayleigh, Mars dust, Venus acid cloud, Titan tholin haze, methane-rich and hycean.
• Leaf colours per spectral type, derived from a pigment model rather than a lookup table — including the purple result for a retinal biosphere.
• Three charts: the surface spectrum, the pigment absorption curves (retinal, chlorophyll and the nitroplast antenna, plus whatever the model selected), and the resulting leaf reflectance with its red edge marked.
• Export to PNG, JPG or PDF as a full data sheet — the landscape plus every number behind it — or the landscape on its own.

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How the colours are computed

Nothing here is art-directed. Each colour is the result of an integral.

Starlight

The star is treated as a blackbody at its effective temperature. Planck's law gives the emitted spectrum, an atmospheric transmission profile attenuates it, and the result is integrated against the CIE 1931 2° standard observer to get tristimulus XYZ, then converted to sRGB through the D65 primaries and the sRGB transfer function. This path is ported from starlight-filter, which uses the same integral to drive a display's gamma ramp.

Because Beer's law is exponential in path length, a lower star simply means the zenith transmission raised to the air mass. That one relationship is why the same model produces a blue noon and a red sunset without being told about either.

Sky, ground and water

A Rayleigh atmosphere scatters short wavelengths out of the beam, so the sky glows with exactly what the beam lost. Dust and haze absorb rather than scatter, so those skies take the transmitted tint instead of its complement — which is why Mars is butterscotch rather than blue.

Ground colour is the total downwelling light (direct beam plus skylight) times a mineral reflectance curve, integrated the same way. Out-of-gamut results are tone-mapped on luminance with the chromaticity preserved, so a deep Rayleigh sky comes out pale blue instead of clipping to flat white.

Vegetation

Photosynthesis is a quantum process, so the model counts photons, not energy. A reaction-centre pigment is chosen by weighing three things against each other:

1. Capture — how many arriving photons the absorption curve takes.
2. Thermalisation — every captured photon is worth 1/λ_trap, because energy above the trap is dumped as heat. This is what stops far-red pigments winning under every star.
3. Cost — a pigment absorbing everywhere is metabolically expensive.

Antenna pigments are then layered on, constrained by what can physically attach to what: a chlorophyll photosystem accepts chlorophyll b, carotenoids and phycobiliproteins, while a rhodopsin accepts only a carotenoid and bacteriorhodopsin runs bare. Phycobiliproteins carry a heavy cost penalty because a phycobilisome can run to half a cell's protein — which is why land plants never took that option, and without it the model paints Earth's forests red.

The leaf's reflectance is what survives that absorption, scaled by a structural reflectance term that reproduces the red edge. Its colour is the illuminant times that reflectance. Calibration check: Earth under the Sun comes out green, reflectance peaking near 550 nm with a red edge at ~705 nm, which is what real vegetation does.

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Honesty about the model

This is a worldbuilding and teaching tool, not a radiative-transfer code.

This is the beginning of the README. Read the rest at the original. Read the full README ↗