Fishing times in Portland, Maine

Moon & sun windows are computed directly from astronomy for your exact coordinates: two daily major periods (moon overhead / underfoot) and two minor periods (moonrise / moonset), per John Alden Knight's 1926 solunar theory. A window is flagged Prime when it overlaps sunrise, sunset, or — if you've added a NOAA station — an actual high or low tide.

Major periods outscore minor ones, and a prime minor can still rank below a plain major, so Prime doesn't mean best. On a day's chart the single highest-scoring window is the gold one, marked Best.

Tide times come from NOAA's free CO-OPS API for the station you set, so they're real predictions, not estimates — but that only covers stations in NOAA's network (mainly the US and territories). Elsewhere you'd need a different tide data source.

The tide curve on each day is drawn between NOAA's published high and low waters by fitting a half cosine across each half-cycle. The peaks and troughs are exact; the shape in between is a very good approximation, but it isn't NOAA's own six-minute prediction. Don't plan a bar crossing by it.

Windows outside 6 AM to 10 PM are discounted when rating a day. The astronomy doesn't care what time it is, but you probably do, so a major period at 1 AM still gets listed and charted while counting for a fraction of a daytime one. That's why the best window shown on a calendar cell is nearly always at a civilised hour.

Solunar theory has a real physical basis (lunar gravity drives tides, and moving water is a well-documented feeding trigger) but the specific claim of sharp 1–2 hour "best window" spikes is folk-science in origin, not a peer-reviewed model — treat the rating as one input, not gospel. Weather, pressure, and species behavior matter too and aren't modeled here.