Solunar theory explained, and how much to trust it

Where the idea came from

The theory was developed and popularised by John Alden Knight, an American angler and writer, who worked on it in the 1920s and published solunar tables in the 1930s. He started from an older folk belief among hunters and fishermen that animals move at particular times linked to the moon. By his own account he considered a long list of things that might influence fish, and concluded that the sun and the moon mattered most. The name joins the Latin words for the two: sol and luna.

Major and minor periods

A solunar table lists up to four periods a day.

Major periods are centred on the moon's upper transit, when it is at its highest point in the sky for your location, and its lower transit, when it is on the opposite side of the Earth. They are conventionally given as about two hours each.

Minor periods are centred on moonrise and moonset. They are conventionally given as about one hour each.

Those lengths are conventions that differ a little between publishers, not measured quantities. The moon takes about 24 hours and 50 minutes to return to the same position in the sky, so the periods fall roughly 50 minutes later each day on average, and now and then a calendar day contains only three of the four.

Many tables also rate whole days. Days close to the new moon and the full moon usually get the highest ratings, and some systems give extra weight when a period falls near sunrise or sunset.

How the tables are calculated

The astronomy is not in doubt. The moon's position can be predicted years ahead with great accuracy. For a given latitude, longitude and date, a program works out the time of moonrise, moonset, upper transit and lower transit, converts them to local time, and places a window around each one.

That is why solunar times are specific to a location. At high latitudes the moon can stay above or below the horizon for a day or more at a time, so on some days there is no moonrise or moonset to mark.

A table can be accurate to the minute about where the moon will be and still be only a guess about what fish will do.

What the evidence says

The original case rested mainly on catch records and observation rather than controlled experiments. Since then, studies looking for lunar or solunar patterns in fish catches and animal activity have produced mixed results. Some have reported a modest association for particular species or settings; others have found none. There is no broad, well-replicated body of evidence showing that solunar periods predict feeding across species and waters.

The question is also hard to test. Catches depend on how many people are fishing, where and how, and anglers who believe in the tables tend to fish at the listed times, which by itself puts more catches inside those windows.

None of that proves the idea wrong. Rhythms tied to the moon and the tides are well documented in many marine animals, and generations of careful anglers have not been imagining everything they saw. The fair summary is that a real effect is possible, that it has not been clearly demonstrated, and that if it exists it is weak enough to be swamped by weather, water conditions and the tide.

Why it overlaps with the tide on the coast

The moon is the main driver of the tide. On coasts with two high waters and two low waters a day, high water follows the moon's transit by a delay that stays fairly consistent for each place. The result is that major periods tend to fall at roughly the same stage of the tide at a given spot, and minor periods at another.

In tidal water, then, the two cannot easily be separated. Moving water has a plain physical effect on where bait collects and where fish feed, so an angler who does well during solunar periods on the coast may simply be fishing a good stage of the tide. Lakes and non-tidal rivers have no meaningful tide, and that is where the theory has to stand on its own.

Using solunar times sensibly

Start with the factors that have a known physical effect: tide and current, wind, weather, water temperature and clarity, and light.

Use solunar periods as a tie-breaker.

Do not cancel a trip because of a poor solunar rating, and never go out in unsafe conditions because of a good one.

Keep a log that includes the blank days as well as the good ones. Over a season it will show whether the periods mean anything on your water.

CatchWindow location pages show the day's major and minor periods and a 30-day solunar calendar. The fishing score combines several inputs, including solunar timing, tide and weather, which reflects the same approach: solunar timing is part of the picture, not the whole of it.

Solunar tables are an honest calculation attached to an unproven idea. Read them, plan around the conditions that are known to matter, and let your own records decide how much weight the periods deserve where you fish.