Solunar calendar: how major and minor bite windows are set
A solunar calendar lists four daily windows when the moon sits in the positions John Alden Knight tied to feeding activity in 1926: two major periods around the moon’s meridian transit, two minor periods around moonrise and moonset. A lunar day runs 24 hours 50 minutes, so every window arrives about 50 minutes later than the day before.
This page explains where those windows come from, how CatchClock computes them, how far the underlying theory has actually been tested, and where a calendar of moon positions stops being the useful thing to look at.
What a solunar calendar is
A solunar calendar is a table of predicted feeding windows, not a record of anything measured. Knight assembled it in 1926 from angler folklore and his own logs, named the two drivers in the word itself — sol for sun, lunar for moon — and set out the case in his 1942 book Moon Up — Moon Down. The calendar answers one narrow question: where the moon is relative to your longitude, and when it next crosses your meridian. Everything else an angler weighs — water temperature, wind, a passing front, how many boats launched at dawn — sits outside the model. Those belong to the wider question of what makes fish feed, which is a different page and a different body of evidence.
How major and minor periods are defined
Major and minor periods are defined by geometry, and the definition is a convention rather than a result. A major period is the two hours centered on a lunar meridian transit — the moment the moon crosses your local north–south line, either overhead (upper transit) or underfoot (lower transit). A minor period is the hour centered on moonrise or moonset. Published tables do not fully agree on the widths: some print one-hour majors instead of two-hour ones. CatchClock uses the most common form and says so, rather than implying that anyone derived the boundary from data.
±60 min / ±30 min
The drift is the part most anglers notice first. A lunar day — one rotation of a point on earth back under the moon — is 24 hours and 50 minutes according to NOAA, so each window lands about 50 minutes later than its counterpart the day before. That drift also means the count is not fixed: across a full year for 39 US cities, 6.8 percent of local days held one major period instead of two, 3.6 percent had no moonrise at all and 3.3 percent no moonset. A calendar that always prints two majors is printing a number, not a computation.
Why the windows are anchored on transit, not peak altitude
The anchor of a major period is the meridian transit, not the moon’s highest point in the sky, and those are not the same moment. Lunar declination moves up to about five degrees a day, so peak altitude drifts away from the meridian crossing — which matters, because peak altitude is what most astronomy libraries hand you and hour angle is what almost none of them do. Measured across 760 culminations at 40 US locations, the peak-altitude shortcut missed the transit by up to 8.6 minutes at lower transit and 8.0 at upper. On a two-hour window that is 7 percent of the window, shifted for no reason.
8.6 min vs 1.1 s
Transit times themselves are not proprietary: anyone can check a date and place against the US Naval Observatory rise, set and transit service. The full list of calls, models and reference checks is written out in how CatchClock computes bite times, including the cases where the engine returns a dash instead of a time.
What a solunar calendar cannot tell you
A solunar calendar cannot tell you whether fish will feed — it can only tell you when the moon reaches a position that a 1926 theory associated with feeding. The distinction is not academic. The largest peer-reviewed test of the idea analysed 341,959 muskellunge catch records from 1970 to 2013 and found the lunar cycle did move catch — by a maximum of roughly 5 percent, and by less than time of day, fishing pressure or water temperature moved it.
≈5%
That is the honest frame for every solunar table on the internet, including this one: a small, real, second-order effect, published to the minute because the astronomy is exact, not because the biology is.
Planning by the solunar calendar
Pick the trip window from lunar transit and moonrise times computed for your coordinates, then work around it.
Fishing the conditions
Pick the window from water temperature, light level, wind direction and a passing front, and ignore the moon entirely.
A solunar calendar is the wrong tool when a stronger driver already owns the day: tide stage on the coast, a front passing through, a spawn in progress, a stocking truck, or a tournament that fixes your hours anyway. Treat the window as a tie-breaker, not a forecast.
How the windows read through all four seasons
The windows are season-blind, and that is the point worth understanding. Lunar transits do not pause in January, and the 24-hour-50-minute rhythm is identical in every month. What changes across the year is how much of each window falls in fishable light, and what the fish are doing while it passes. Winter is not a gap in this table: on the Minneapolis bite windows ice covers the lakes while walleye and crappie keep feeding beneath it, and on the Phoenix fishing forecast the cool months are the comfortable season, with trout stocked into urban lakes while summer fishing moves to after dark.
| Season | Where the windows fall | What the water is doing |
|---|---|---|
| Spring | Daylight grows fastest around the equinox — 2–3 minutes a day at mid-latitudes — so a larger share of majors lands in fishable light each week | Warming water lifts feeding rates; spawning movement in bass, walleye and crappie overrides any lunar signal |
| Summer | Longest days: about 15 hours 40 minutes at 45° N near the June solstice, so both majors usually fall in daylight | Midday heat pushes fish deep; the first and last hour of light often beats the calendar outright |
| Fall | Daylight shrinks at the same equinox rate of 2–3 minutes a day, and majors drift out of the hours most anglers can fish | Cooling water and lake turnover drive feeding in pike, muskellunge and walleye; wind sets up more than the moon does |
| Winter | Shortest days: about 8 hours 45 minutes at 45° N near the December solstice, so often one major of two is fishable in light | Ice fishing across the northern tier, steelhead in Great Lakes tributaries, stocked trout in the desert Southwest, peak comfort in Florida |
Open seasons, size limits and license rules differ by state and change from year to year, so this site does not reproduce them; the current rules come from the state fish and wildlife agencies directly.
How to read a calendar for your own water
A solunar calendar is right for one place at a time, because meridian transit is a longitude event. The earth turns 15 degrees an hour, so one degree of longitude is four minutes of transit time. Across the 39 US cities in the CatchClock data grid, 96.4 percent of the 741 city pairs differ by more than ten minutes on the same date — which is why the city fishing forecast hub publishes a table per city instead of one national schedule. Latitude works differently: it barely moves transit times, but it stretches moonrise and moonset, so minor periods vary far more between Anchorage and Tampa than majors do.
Two adjustments make the calendar usable. On coastal water, read tide stage first and the lunar window second — where they disagree, the tide usually wins. And if you want the windows on a phone at the water rather than on a screen at home, the fishing app comparison sets out which tools do that, and where each of them falls short.