Moon phase vs. solunar windows — two different tools
Moon phase and solunar windows are related but measure different things. Moon phase describes the character of the overall lunar period — whether nights are bright or dark, whether tidal swings are at their maximum or minimum, and whether you're heading into or out of a historically productive feeding cycle.
Solunar windows describe the precise timing within any given day when feeding activity is most likely — the major transit windows and minor rise/set windows. These occur regardless of phase.
The most useful combination: use moon phase to plan which days to prioritize, then use solunar windows to plan which hours within those days to be on the water and fishing actively.
The spawn — bass and the moon
Largemouth bass don't spawn on a calendar date — they spawn when conditions align: water temperature in the 65–72°F range, and a lunar cue. The prevailing theory is that bass use the moon as a synchronization signal so that males (who build nests and guard fry) and females (who move on after laying eggs) are ready simultaneously.
Most fisheries biologists and guides agree that the heaviest spawning activity occurs on new and full moon periods in spring once water temperature has reached the spawning threshold. The full moon in April or May (depending on latitude) is often when the largest females are found shallowest and most vulnerable.
In your Bassai log, this shows up as a cluster of shallow catches with GPS coordinates in 2–6 feet of water, often on hard bottom (gravel, shell, clay) in protected coves, during the first full or new moon after water temperature crossed 65°F. Over multiple seasons, the pattern across the same water body should be strikingly consistent.
Seasonal amplifiers — when moon phase × season compounds
Moon phase alone is a modest signal. But certain combinations with season produce outsized results:
Full moon in October. The fall feed coincides with the full moon's strongest gravitational and nocturnal light effect. Bass that are already in aggressive feeding mode for winter preparation become even more active. Many experienced anglers consider the October full moon the single best week of the year for catching large bass.
New moon in early spring. The first new moon after water temperature crosses 55°F is often the trigger for pre-spawn staging. Fish move up from deep winter structure and begin positioning near spawning areas. They're catchable in the 6–15 foot transitional zone — deeper than spawn depths but shallower than winter locations.
Full moon in late June. The post-spawn recovery period on a full moon often produces some of the year's largest female bass. They've recovered from spawning and are feeding aggressively again, positioning in the 8–15 foot range on main-lake structure. Night fishing during this window, around the full moon's major solunar windows, is where trophy-sized fish are caught most consistently.
How Bassai stores moon phase
Moon phase is stored as a decimal value from 0.0 (new moon) to 1.0 (new moon again, after a complete cycle), with 0.5 representing full moon. The named phase — New Moon, Waxing Crescent, First Quarter, Waxing Gibbous, Full Moon, Waning Gibbous, Last Quarter, Waning Crescent — is also stored for human-readable display. Both values are recorded at the time of each catch, computed from the catch's exact timestamp.