EXP-001instrumentLiveSVG · One number · A sun you can drag

Nightfall.

Six paper ridgelines, a sun, a moon, and one control: the hour. Drag across the box and the sun walks down the sky, sets behind the far ridge and keeps going; the moon rises opposite it, the greens turn to slate and then to almost nothing, the birds go home, the mist settles in the folds and the fireflies come out. Stand still in the dark and they come to your cursor. Gather enough of them and they start blinking together.

A lightbox with an evening in it.

Drag across it to move the sun. Everything else in the box follows.

The hour

Bench notes

One number: Nothing in the scene has a colour of its own. A position on the slider becomes a clock time, the clock becomes a solar altitude, and every value in the box is read off that altitude: six ridge fills, the sky gradient, the horizon glow, how much mist, how many stars, whether the birds are still flying. Change the hour and thirty-odd values move at once, in agreement, because there is only one thing to disagree with. That is the same discipline as a design token, run at sixty frames a second.
Honest sky: The twilight names on the clock are the real ones: civil light ends six degrees below the horizon, nautical at twelve, astronomical at eighteen. The sun crosses the far ridgeline at exactly zero, because the ridge and the sun are drawn in the same coordinate space. The moon rises as the sun sets and sets as it rises, which is not a flourish; that is what a full moon is.
Fireflies keep time: Real fireflies phase-lock. A field of Photinus carolinus starts as noise and ends up pulsing as one animal, each one nudging its own clock toward its neighbours. These do the same: every fly carries a phase and its own natural rate, and the closer it gets to your cursor the harder it is pulled toward the average of the crowd around you. Nobody is conducting. The pulse is what happens when enough of them are listening to each other.
The manners: The whole scene is server-rendered SVG, finished and correct before any script runs, so a page with no JavaScript still gets a forest at nightfall. Only horizontal drags are claimed, so scrolling past it on a phone always works. With reduced motion on, the instrument stays: the slider, the presets and the drag all still move the sun. What goes away is everything that moved on its own.