About LuNAC
A calendar that begins with the Moon.
LuNAC is a lunar calendar and astronomical almanac that organizes time around the Moon’s cycle. Each month begins at the astronomical new moon, with lunar days leading the calendar and familiar Gregorian dates alongside them. Moon phases, celestial positions, and sky events provide the reference. Your observations make the record personal.
LuNAC offers a way to follow time through something you can observe: the changing Moon, the movement of the planets, and the return of the seasons.
How the lunar calendar works
In LuNAC, a month follows one complete cycle from an astronomical new moon to the next.
Start with the current lunar day. See the Moon’s phase and illumination, explore the month in the calendar, or follow celestial events in sequence on the timeline. Move between a single moment and the wider cycle to see how the sky changes over time.
Gregorian dates remain alongside lunar days, connecting the lunar month to everyday plans.
Follow the sky through the month
LuNAC brings together Moon phases, positions of the Sun and planets, eclipses, and other celestial events. It shows celestial positions against the actual astronomical constellations, including Ophiuchus.
Explore what is happening now, look ahead to an event, or return to a moment you recorded. Event times give you a reference for following the sky from one lunar day to the next.
Keep your observations beside the astronomy
An almanac becomes more personal when it includes what you notice.
Record a sighting of the crescent Moon, a change in your garden, the conditions during a night of stargazing, or something from your daily life you want to revisit. Keeping observations alongside the lunar calendar gives you a way to compare experiences across cycles and build a record over time.
The astronomical data describes the sky. Your notes preserve your experience of it. What those observations mean to you remains your own.
How LuNAC calculates the sky
LuNAC uses Astronomy Engine (astronomy-engine) to calculate celestial positions and events. Its planetary calculations include truncated VSOP87-series models. Astronomy Engine tests its results against independent astronomical references, including NOVAS C 3.1 using the DE405 ephemeris and JPL Horizons. VSOP87 supplies a mathematical model for planetary motion; NOVAS and JPL Horizons provide independent results for comparison.
The computations are deterministic: with the same model and inputs, they produce the same result. LuNAC organizes that astronomical information into lunar days, calendar views, and a timeline. Event times are established in Coordinated Universal Time (UTC) and shown in local time where useful.
LuNAC also keeps provenance with its results, including the method, timestamp, and observer context. You can see what a value represents and trace how it was obtained.
Explore LuNAC your way
Use the app to follow lunar days and keep personal observations. Explore the sky through the web calendar and timeline. Follow a whole lunar month on the pages of the printed almanac.
Each format brings you back to the same idea:
The Moon defines the month, the sky provides the reference, and your observations build the record.
Welcome back to the sky.