Everything it does the rest of the time, because nothing is ever fetched. Positions are computed on the device from the date, the time and your coordinates, so the calendar opens in airplane mode, in a valley with no signal, or on a boat. No account, no login.

The iOS build, listed as Moon Phase Calendar Offline, is 35.4 MB, needs iOS 13.0 or later, runs on 130 device models and ships in 44 App Store languages. The Android build is listed simply as Moon Phase Calendar and was last updated on 27 July 2026. Its Data safety card declares no data shared with third parties and no data collected. Install it from the App Store or Google Play.

That line is from the app’s own App Store description. The Play Data safety card is the part of it a stranger can check.

Accurate enough that the arithmetic is not the weak link. NASA puts the cycle of phases at about 29.5 days and lists eight lunar phases in order; the US Naval Observatory names the same eight traditionally recognized stages starting from new moon. Both are closed-form problems: given a date and a position, illumination and rise and set times follow from published series expansions.

That is why Moon Phase Calendar can cover 1900 to 2100 — 201 years — without downloading a byte. The listing credits the Meeus astronomical algorithms. What that buys you is consistency: the same date returns the same answer on a plane as at home. What it does not buy you is sky conditions, because cloud cover is weather rather than astronomy, and this app does not forecast it.

They are defined by how far the sun sits below the horizon, and the definitions are not the app’s own. The US Naval Observatory sets civil twilight at the moment the centre of the sun is 6 degrees below the horizon, nautical twilight at 12 degrees and astronomical twilight at 18 degrees. Sunrise and sunset are computed at a geometric zenith distance of 90.8333 degrees, which is 50 arcminutes below horizontal: the sun’s 16-arcminute apparent radius plus 34 arcminutes of average refraction.

The dark-sky window in Moon Phase Calendar is the overlap of two of those facts — the stretch of astronomical night during which the moon is also below the horizon. For deep-sky photography that window, not sunset, is the number that decides the trip, and around a full moon it can be zero minutes long.

Not the standing most people assume. Moon Phase Calendar classifies each day as a root, leaf, flower or fruit day following the Maria Thun convention used on many biodynamic farms. The standard those farms are actually audited against is the International Demeter Biodynamic Standard, whose 2025 English edition runs to 204 pages and asks for the consideration of cosmic rhythms in plant production and animal husbandry.

That phrase appears exactly once. Search the same 204 pages for moon, lunar, zodiac, constellation or Thun and every one of those searches returns zero hits. Root and leaf days are therefore a gardening tradition the standard leaves room for, not a rule certification enforces. The app presents them as a planning convention, and that is how gardeners should read them.

That eclipse is why a lot of people install a lunar calendar this year. NASA’s eclipse pages give a greatest duration of 6 minutes 23.2 seconds on the central line as the path crosses southern Europe and North Africa, and note that the prediction ignores the lunar limb profile, so edge-of-path timings are approximate.

Moon Phase Calendar carries eclipse path visualisations for 2024 to 2030 on the device, next to supermoons, blue moons and eight annual meteor showers rated for moon interference. Get Moon Phase Calendar Offline on iPhone or Moon Phase Calendar on Android before you travel, because good eclipse ground rarely has coverage.

All three alternatives below were checked live on 18 September 2026. All are free on iOS.

When you need a forecast rather than an ephemeris. It will not tell you whether clouds will ruin tonight, and My Moon Phase is the better install for that. It has no horoscope, no natal chart and no cycle tracking, so anyone shopping for those should skip it.

Two other honest limits. The Play listing shows 100+ downloads and the iOS build is still version 1.0 with no user ratings, so there is no track record to lean on. And the solunar windows come from Knight’s solunar theory, which is an angling planning heuristic rather than a tested prediction of what fish will do.

An offline lunar calendar that computes phase, illumination, rise and set, twilight bands and solunar windows on the device for any date from 1900 to 2100, in 35.4 MB. It is the right pick when the signal will not be there and the planning is practical — gardening, fishing, dark-sky photography, eclipse travel. It is the wrong pick if you want a cloud forecast or astrology, both of which rivals do better, and it arrives without the ratings history those rivals have.