# Syna daily, monthly and yearly forecasts

The forecast compares moving planets with the individual's natal Sun, Moon,
Mercury, Venus and Mars. It uses the same geocentric apparent tropical positions
as Syna's birth-chart engine (Astronomy Engine 2.1.19). Birth date, recorded local
time, birthplace coordinates and historical IANA time zone determine the natal
chart. The chosen reading time zone determines forecast calendar boundaries.
It defaults to the browser time zone and can be changed independently.

Daily: one snapshot at local noon on the selected date. The ten transiting bodies
are Sun, Moon, Mercury, Venus, Mars, Jupiter, Saturn, Uranus, Neptune and Pluto.
This is not a list of every transit happening during that day.

Monthly: samples every six elapsed hours from the start of the local calendar
month, plus the last millisecond before the next month. The transiting Moon is
omitted because its fast contacts are better suited to the daily view. The natal
Moon remains included when the birth time is known. Calendar months, leap days
and historical daylight-saving transitions are handled with Temporal.

Yearly: the complete January–December calendar year in the selected reading time
zone. Samples are taken every six elapsed hours, plus the final instant. This
editorial view focuses on transiting Jupiter, Saturn, Uranus, Neptune and Pluto
for longer-term themes, omitting the faster-moving Sun, Moon, Mercury, Venus and
Mars. They are still available in daily/monthly readings. The annual overview
retains the closest sample per planet/aspect pair across the entire year. The
12-month guide independently selects the closest sampled contact within each
local month from those same annual samples. Long-lasting or repeating patterns
can therefore appear in several months. These dates are not exact transit peaks.

Five major aspects are used: conjunction (0°), sextile (60°), square (90°), trine
(120°), opposition (180°). All have a maximum 2° orb. This is an explicit editorial
choice, not a universal astrological standard. The smallest angular separation
handles the 0°/360° wrap. For unknown birth times, the natal Moon is excluded;
other contacts require orb plus the natal birth-day uncertainty to fit within 2°.
Angles, houses and natal outer planets are not used in these forecast meanings.
The result's birth-chart summary also displays the natal rising sign when a birth
time is known, plus an expandable list of all ten natal planet positions. The
summary labels possible signs and noon reference positions for unknown times;
these additional displayed placements do not change the forecast meanings.

Contacts are ranked by smallest orb. Each of the five reflection themes uses
the closest qualifying contact to its associated natal planet. A monthly report
keeps only the closest sampled occurrence of each distinct planet/aspect pair;
it does not list every repeated retrograde crossing. A six-hour sample can miss
or misdate a very brief contact at an orb boundary. Dates are therefore labelled
as closest samples, not exact peak times or predicted events. Slowly moving
contacts can remain active before or after the selected month or year.

Birth details are validated with the existing chart engine. Forecast selection
supports 1900–2100. Samples before the birth instant are excluded for a month or
year that overlaps the birth date. The yearly guide labels pre-birth months and
does not generate readings for them. A day with noon before the birth is rejected.

Original authored text combines the transiting planet's symbolism, the natal
planet's theme, and the aspect's traditional meaning. There is no AI API, event
prediction, percentage score, or claim of scientific validity. The same inputs
produce the same results. All astronomical computation runs in a browser worker.
The forecast does not save or send birth details. Only city search queries go to
Open-Meteo/GeoNames; forecast questions or names are not part of those requests.

Sources for the calculation method and conventional transit framework:
- Astronomy Engine (MIT): https://github.com/cosinekitty/astronomy
- Astrodienst, Transit: https://www.astro.com/astrowiki/en/Transit
- Astrodienst, Transits FAQ: https://www.astro.com/faq/fq_fh_transits_e.htm
- Temporal documentation: https://tc39.es/proposal-temporal/docs/
- Open-Meteo geocoding: https://open-meteo.com/en/docs/geocoding-api

Source: src/forecast-engine.mjs. Browser worker: src/forecast-worker.mjs.
The bundled worker, UI and this method file are stored with the static site.