Where the data comes from

Source	Licence	Used for
NOAA Space Weather Prediction Center	US federal government work, public domain	Kp index, the three-day forecast, OVATION overhead probability
Finnish Meteorological Institute	CC BY 4.0	Magnetometer network, HARMONIE cloud forecast
Fintraffic / digitraffic.fi	CC BY 4.0	Road cameras, road weather stations, road condition forecasts, traffic messages
Computed on this site	—	Sunrise, sunset, twilight, the light band, moon phase and altitude

Data source: Fintraffic / digitraffic.fi, licence CC BY 4.0

Checked, and not used

FMI's all-sky aurora cameras. The obvious thing to put on an aurora page is a picture of the sky, and we cannot. Auroras Now! serves its front page, but the image pages behind it return 403 Forbidden — to a command-line fetch and to a real browser alike, so it is a server rule rather than a bot block. There is no openly available image to embed, so every aurora page links to Auroras Now! instead and says why.

Ski resort, hotel and port cameras. Levi, Ylläs, the Port of Helsinki and the Port of Turku run their own cameras under their own terms, and none of those terms allow a third party to embed the picture. They are links in the camera gallery, never images.

The Helsinki events calendar. The City of Helsinki's Linked Events API answers and carries 16,928 events. The event data is CC BY 4.0; individual descriptions and images are not necessarily, and each record carries its own licence field. Until that is handled per record the calendar is not published — see events.

Two things we measured rather than guessed

FMI publishes the magnetometer network in hourly batches. The newest reading is between zero and about sixty-five minutes old by design, whatever window you ask for. The staleness threshold on this site is set from that measurement; the round number it started at silently deleted the site's best local signal for most of every hour, with the feed working perfectly and nothing on the page saying why.

Fintraffic's reliability field is not about reliability. It says whether a roadside station fed a particular forecast row, and on most Finnish roads none does — 2,092 of 2,137 rows on road 4 on the day we measured. Treating it as a quality gate deleted the entire road-condition forecast from every page. It is now used for exactly one thing: deciding whether a reading is labelled measured or modelled, which is a distinction worth a word on a page about a road you are about to drive.

The full version of this page, with every endpoint, gotcha and failure behaviour, is DATA_SOURCES.md in the repository.