Tsukigoyomi shows you tonight's moon, its age, and its traditional Japanese name the moment you open the app. Use the tabs at the bottom to switch between Tonight's Moon, the monthly Calendar, and the name Encyclopedia.
Moon age, phase, and illumination are computed from established astronomical formulas and closely match the real moon. Because the app tracks the moon's phase itself rather than local rise and set times, the display is accurate wherever you are.
Yes — every feature works completely offline. Moon ages, names, and tide names are all calculated inside the app, so it works in airplane mode, deep in the mountains, or far out at sea.
Neither. The app requests no permissions at all, and there is no sign-up or login. Install it and start using it without handing over anything.
In old Japan, the moon of each lunar-calendar night had its own name. Izayoi, the "hesitating moon," rises reluctantly the night after the full moon; Tachimachi-zuki is the moon you "stand and wait" for as it rises later each night. The app displays one of 17 such names every day.
Tide names describe the strength of the tides based on the moon age. Around the new and full moon, the difference between high and low tide is greatest — the "spring tide" (o-shio) — and these names have long been used in Japan to time fishing and clam digging.