Sky observations

How it knows.

Sol records its sunset forecast before the evening it describes. Every nightly update that reads the cloud forecast is kept as its own file, named by the instant it was issued and never rewritten, so a forecast can be read back later without anyone being able to move it. The scoreable part of that archive is published at /history/calls.json: for each city and each evening, the last forecast issued at least an hour before that evening’s sunset. A forecast made in the last minutes before a sunset is a nowcast and would flatter the record, so it is not kept, and a later issue can never displace a real forecast.

The rule, in words. An evening is scored only if three things are true: Sol has a forecast on file for that place and evening, the forecast was issued at least an hour before that sunset, and you recorded yours after it. Both sides sit on the same four steps: 1 little colour, 2 some colour, 3 good colour, 4 exceptional colour. The score of one evening is what you saw minus what was forecast. Zero is exact; one step either way is close, and close counts the exact ones with it; two or more is a miss. The direction is kept, because the forecast was too high when it promised more colour than the sky gave, and too low when the sky gave more.

Which forecast an evening is scored against. Sol updates a fixed set of cities every night, so a forecast exists for those places and no others. When you stand somewhere else, the page uses the nearest of them, and only if it is within 75 kilometres, near enough to be under one evening’s weather; it prints that city and the distance beside the evening. Further out, the evening is still yours to keep. It simply is not scored.

What this cannot establish. Not that Sol is accurate. You choose which evenings to record, so the sample selects itself; you can see the forecast before you rate the sky, so nothing here is blinded; and one person’s “good colour” is not another’s. Nothing is pooled: your evenings are yours alone. Under twenty scored evenings the page prints counts and refuses to print a rate.

Where an evening is kept. Signed out, in this browser’s own storage alone, gone if you clear the site’s data. Signed in, on your account, readable by you and by nobody else. Every evening carries a Remove of its own. Publication is opt-in per evening and off unless you turn it on; today it only marks the record, because there is nothing published to join yet. Photographs are not taken in this version: there is no server to receive them, and publishing other people’s pictures asks for consent and moderation done properly or not at all.

Issued forecasts, as JSONHow Sol calculates light