[craig-o-curtis]

What

The landing page gets a realistic aurora over a real night sky, seen from one of two places:

• Ísafjörður, Iceland: from Sólgata by the church, looking north-northeast past the Eyrarfjall wall to the fjord mouth.
• Helsinki, Finland: from the Suomenlinna main pier, across the water to the city skyline.

The first site comes from the browser's time zone: Finland opens on Helsinki, Iceland on Ísafjörður, and anywhere else gets a random site. A faint ⓘ in the bottom-right corner opens a popover with the site's details, the data credits and a location switcher.

How it works

Everything renders in a Web Worker on an OffscreenCanvas, so the main thread does no WebGL work. The page's own script is 1.6 KB.

• Aurora (simulated): a thin emissive curtain about 100 km up, drawn in perspective over a curved Earth (after Lawlor & Genetti: a ground footprint times a height profile). Rays converge toward the magnetic zenith. Folds, bright knots and dark gaps vary along the arc.
• Stars (real): the Yale Bright Star Catalogue, V ≤ 5.5, precessed to date and placed for the current time and site.
• Moon (real): its true position, including the parallax correction for the viewer's location, and its phase lit by the real sun, at true size. It is hidden by the mountains when behind them and reflected in the sea at Helsinki.
• Ground:
  • Ísafjörður: a mountain skyline from Copernicus DEM GLO-30.
  • Helsinki: the city skyline from OpenStreetMap, including its 3D building parts, so the Cathedral and other landmarks keep their domes and spires. The city has lights and a glow, and the sea reflects the sky.
• Phones: on portrait screens the view widens and tilts so the aurora shows above the cards rather than behind them.
• Time: taken from @northguild/gmt. getUnixNow gives the clock and getSystemTimeZone picks the starting site, both in the worker so Temporal stays off the main thread. Date is now banned in lint by @northguild/gmt-oxlint.
• Data provenance: the scripts in scripts/ regenerate every data file (skylines, stars.bin, the moon map).

Commits

1. fix(theme): the glass hairline (.gmt-glass::before) drew round corners outside the bevel. It now inherits corner-shape.
2. chore: add the @northguild/gmt dependency and the Date ban, plus dev dependencies for the data scripts.
3. build: site definitions, data scripts and generated data.
4. feat(site): the renderer, the shaders and the info popover.
5. feat(site): pick the starting site from the time zone, give the site buttons the sonar ping, frame phones properly.
6. feat(helsinki): domes and spires from OSM 3D building parts, with Helsinki sampled every 0.05°.

Checks

• oxlint, oxfmt --check, pnpm -r check and pnpm -r build pass locally.
• Time zone defaults, tested with Playwright time zone emulation:
  • Europe/Helsinki opens on Helsinki.
  • Atlantic/Reykjavik opens on Ísafjörður.
  • America/New_York gets a random site.
• GPU: about 1.7 ms per 1280×720 frame on an M-series Mac, the same as the earlier 2D shader. A 12-step fallback runs in about 1.1 ms.
• Motion is calm: under 1% of pixels change over 1.5 s.
• Reduced motion draws one still frame (verified with two frames 3 s apart).
• The worker bundle is 75 KB gzipped. About 46 KB of that is the Temporal polyfill that @northguild/gmt bundles. It loads after the page is idle and runs off the main thread.

Known limits

• Roof shapes are only as good as the OSM 3D modelling. The Cathedral is modelled in detail; most other buildings are flat-topped blocks at their mapped height or floor count.
• The aurora is simulated, not live space-weather data.