Lunar calculations · ChronOS guide
Moon phase API for lunar state and event timelines
Moon phase is determined by the angular relationship between the Sun and Moon as seen from the selected model origin. A production API should distinguish instantaneous phase state from the time of a named phase event such as new moon or full moon.
01 / Method
Phase angle, illumination and named phases
The lunar phase cycle is continuous. Labels such as waxing crescent or waning gibbous describe intervals, while new moon, first quarter, full moon and last quarter are event instants defined by target elongations.
ChronOS exposes lunar state through its ephemeris and event contracts. Search windows are half-open and event results are refined numerically, preventing duplicate boundary events when adjacent windows are combined.
- Sun–Moon elongation
- Waxing or waning state
- Illuminated fraction where requested
- Typed main-phase event searches
02 / API example
Request Sun and Moon state
The exact-instant ephemeris is the base request for deriving a lunar phase state. Typed events are searched with POST /v2/events/search.
curl --request POST \
--url https://api.chronos-ephemeris.com/v2/ephemeris \
--header "Authorization: Bearer $CHRONOS_API_KEY" \
--header "Content-Type: application/json" \
--data '{
"datetime_utc": "2026-07-16T12:00:00Z",
"bodies": ["sun", "moon"],
"include": ["physical_phenomena"]
}'Keep API keys in server-side secret storage. The example uses an environment variable and contains no production credential.
03 / Evidence
Accuracy of lunar events
Moon calculations are especially sensitive to the selected lunar model and time scale. Event validation should compare unrounded instants and state the event definition, not only a formatted local date.
ChronOS returns calculation metadata and publishes release evidence so an application can trace changes after an engine or dataset update.
04 / Applications
Moon phase applications
Lunar state can drive calendars, educational displays, notification systems and astrology workflows. Local moonrise and moonset are separate observer-dependent horizon calculations.
- Lunar calendars
- Moon phase widgets
- New and full moon notifications
- Astronomy and astrology timelines
05 / FAQ
Frequently asked questions
Is Moon phase dependent on location?+
The global phase geometry is not location-dependent, although the local date, moonrise, moonset and apparent horizon position depend on observer location and timezone.
Can ChronOS find the next full moon?+
The typed event-search contract supports lunar phase searches within an explicit UTC time window.
Is illumination the same as phase angle?+
No. They are related values, but the geometric phase or elongation and the visible illuminated fraction are not interchangeable fields.