Piece one — live sky

Tonight’s aurora

This sky is not a recording. It is driven by the planetary K‑index — the number aurora hunters watch — as it stands right now.

Reading the sky…

The aurora above emits at a handful of exact wavelengths, and this site’s palette is drawn from three of them. Find them below.

Piece two — an instrument

The visible spectrum

400 to 700 nanometres. Every colour here is computed live from the CIE 1931 colour-matching functions — measured human vision, not a lookup table — and pressed into the screen’s gamut without bending its hue.

Normalised lifts the dim ends so every hue is visible. True luminance shows how bright each wavelength really looks to the eye — greatest near 555 nm, falling to near-black at both ends.

The visible spectrum as a horizontal band: deep violet at 400 nanometres through blue, green, yellow and orange to deep red at 700.

557.7 nm

#81da00 oklch(0.800 0.225 132.7)

The strip above is the full spectrum, rendered at build time from the same colour math the interactive handle uses. Turn JavaScript on to drag through it.