Changelog

All notable changes to this project are documented here. The format follows Keep a Changelog, and this project adheres to Semantic Versioning.

Unreleased

Reworded the package description. The previous wording listed "biodynamic cycles" alongside the astronomy, which reads as an endorsement of the tradition rather than a description of what the library computes. It now leads with the verifiable ephemerides and attributes the declination cycle to the calendars that use it, matching the separation the README and the GreenCal moduledoc already draw.

No code changes: 0.1.0 and 0.1.1 are functionally identical.

First release.

GreenCal.day/3 — everything about one civil day at one location: sun rise/transit/set with azimuths, time above the horizon, twilights, moon rise/transit/set, phase, illuminated fraction, distance, declination, node crossing, and the constellation the Moon stands in.
GreenCal.calendar/3 — one day per date of a range, with parallel: true to spread independent days over the schedulers.
GreenCal.lunar_events/2 — exact instants of the events a printed lunar calendar marks with a symbol: phases (with an eclipse screening flag), perigees and apogees, node crossings, and lunar standstills.
GreenCal.constellation_of/3 — equal-sector sidereal zodiac (Lahiri ayanamsa) by default, or the real unequal IAU boundaries with boundaries: :iau (13 constellations, Ophiuchus included), the convention printed biodynamic calendars use.
The three independent lunar cycles kept distinct: waxing/waning (illumination), ascending/descending (declination), approaching/receding (distance).
Low-level astronomy is public: GreenCal.Astro (UT-facing facade), GreenCal.Astro.Sun, GreenCal.Astro.Moon, GreenCal.Astro.RiseSet (generic crossing finder over any body) and GreenCal.Astro.Time.
Options: :elevation, :time_zone, :twilight, :boundaries, :delta_t, :parallel.

Zero runtime dependencies, and no time zone database needed unless :time_zone is used.
Rise/set by numeric search, not the closed-form hour-angle formula: the latter assumes a constant declination and can be more than 15 minutes off for the Moon. Crossings shorter than the sampling step are caught by probing the culmination, so a 55-minute polar day is found rather than reported as polar night.
UT and TT are kept apart (jd vs jde), converted in one place. ΔT uses observed IERS values over 2000–2026, the Espenak & Meeus polynomials before, and a documented hold-then-bridge extrapolation after.
Degenerate cases are reported, not faked: :always_above / :always_below states, and a nil moonrise on the ~1 day per month the Moon does not rise.
Astronomy and tradition are labelled apart. Rise/set times, phases and declination trends are validated against published references; elements, organs and sowing days are presented as the tradition they are.

Meeus, Astronomical Algorithms (2nd ed.), examples 7.1, 12.a, 12.b, 22.a, 25.a, 28.b and 47.a — the complete chapter 47 tables reproduce example 47.a to 0.13″ in longitude and 0.03 km in distance.
USNO rise/set API for moonrise/moonset at Paris, Sydney and Edinburgh, within 30 s (the USNO publishes whole minutes).
Published 2026 phase instants, and all four 2026 eclipses found by the screening flag with no false positive over the year.
Property tests and physical invariants (bounded distance and latitude, event ordering, chained daily windows equal to one continuous search).