Observatory — 51.50°N, 0.12°W · Europe/London
An observatory for sun, tide and slow signals. Every arc, hour and shadow below is calculated where you stand — not fetched. Drag time. Watch the day fold.
NOAA solar equations · Meeus moon · All in-browser. How it’s made →
Four moments that frame the day. Times in local clock. Twilight is not decoration — it decides what you can see.
| Event | Clock | Solar | Note |
|---|
Meeus truncated. Good to ~1°. For tide-watching, not navigation.
Golden hour is when the sun is 6°–−4° below horizon to 6° above. Blue is the 20 minutes after sunset before civil ends. The numbers shift fast near equinox.
At this latitude the day length changes ~3m 40s per day near equinox, ~25s near solstice. If you log it daily, the curve looks like a sine wave standing on its shoulder.
Not the next meeting. The next time the light returns to where it was.
Sun position uses the NOAA Solar Calculator (Meeus-adjacent). Given latitude, longitude and date, we solve declination and hour angle on the device. No weather API, no sunrise service. The sky gradient is a lerp between measured palettes keyed to solar elevation: −12°, −6°, −4°, 0°, 6°, 20°, 45°, 62°.
elevation = asin(sin φ·sin δ + cos φ·cos δ·cos H)
The sky is a 720×420 canvas repainted on scrub. No blur, no aurora blob. Just three stops interpolated in oklab and a 0.6px film grain drawn once. It’s 5 draw calls.
Clock time follows your timezone; solar noon does not. Walk 1° east and solar noon arrives 4 minutes earlier. The ledger shows both so you stop confusing them.
Print taught us: a rule, a margin and a number set right are enough.
Single HTML file, one CSS, one JS, two font families, zero framework. First paint is the content — the canvas is progressive. prefers-reduced-motion respected; scrubber is keyboard accessible (arrow keys ±5 min, PageUp/Down ±60). Offline-capable after first load.