---
title: "Secondary Progressions & Solar Arc (推運與太陽弧)"
method: GET
path: "/api/trpc/progressions.calculate"
tags: ["Western"]
---

# Secondary Progressions & Solar Arc (推運與太陽弧)

`GET /api/trpc/progressions.calculate`

## Request

- Base URL: `https://api.asktian.com`
- URL: `https://api.asktian.com/api/trpc/progressions.calculate`
- Auth: HTTP bearer

Western predictive astrology — the catalogue's first forecasting engine, answering 'what is being activated THIS year?' from the birth chart. THREE linked time-techniques: SECONDARY PROGRESSIONS (the 'a day for a year' clock — the real sky advanced one day per year of life, giving the progressed Sun ~1°/yr, the progressed Moon a sign every ~2.5 yr, the progressed Ascendant/Midheaven by the Naibod key, and the 8-phase progressed lunation cycle); SOLAR ARC DIRECTIONS (the whole chart advanced as a rigid body by the solar arc ≈1°/yr, with the directed→natal contacts and the date each perfects — 1° of arc ≈ 1 year); and the SOLAR RETURN chart (the moment the Sun returns to its exact natal longitude each year, Newton-solved to the arc-second, with the Solar-Return Ascendant as the headline of the year ahead). Tropical zodiac. The astronomy is firm; the timing is symbolic — it does NOT calculate lifespan. Verified against Prince William's solar-arc Saturn (0° Scorpio at age 15.2, 1997).

Cost: 7 TIAN Points per call. tRPC procedure `progressions.calculate`.

## Query parameters

- `input` string

## Response `200`

tRPC result envelope

- TrpcResult: tRPC HTTP response envelope.
  - `result` object
    - `data` object: The procedure's return value (system-specific).

---

[API](https://skmtc.dev/asktian/apis/asktian-metaphysics-api.md) · [All operations](https://skmtc.dev/asktian/apis/asktian-metaphysics-api/llms.txt) · [OpenAPI document](https://skmtc.dev/asktian/apis/asktian-metaphysics-api/revisions/3c8fdc979206?raw)