What color is a star?
An interactive blackbody-radiation explorer. Pick a temperature to see the Planck spectrum, the color and brightness a human eye would actually see, where that color sits on the CIE 1931 color map, and the math behind it.
- v2 (the current site,
/): a dependency-free rewrite. It has three color models: the original simple one, CIE 1931 colorimetry, and colors of real stars from model spectra (Harre & Heller 2021, with the sRGB gamma correction applied). Brightness follows human vision, so cold objects go black instead of red. Each page ships as a single ~25 KB file.
- v1 (
/v1/): the original 2023 Create React App version, kept as it was.
Running it
npm install
npm run build:v2 # v2 only -> build/
npm run build # v1 into build/v1, then v2
python3 -m http.server 4173 --directory build
npm run test:v2 # physics and slider-scale tests
v1's dev server is npm start.
Layout
v2/: pages, partials, source, data and tests for the current site. See CLAUDE.md for a map.src/, public/: v1.docs/v2/PLAN.md: the v2 plan, including the v1 math audit, data sources, verified reference values and open questions.docs/WHY.md: why things are the way they are.
Data sources
- CIE 1931 2° standard observer color matching functions (CIE, doi:10.25039/CIE.DS.xvudnb9b).
- Harre & Heller (2021), "Digital color codes of stars", Astronomische Nachrichten, arXiv:2101.06254.
- Hollands et al. (2026), "Any colour you like: the diverse chromaticities of white dwarfs", RAS Techniques and Instruments, doi:10.1093/rasti/rzag069.
