---
title: "Astronomical Tidal Forcing"
method: GET
path: "/tidal/forcing"
tags: ["tidal"]
---

# Astronomical Tidal Forcing

`GET /tidal/forcing`

## Request

- Base URL: `https://api.openephemeris.com`
- URL: `https://api.openephemeris.com/tidal/forcing`
- Auth: one of:
  - HTTP bearer
  - API key in header `X-OpenEphemeris-API-Key`
  - API key in header `X-API-Key`
  - API key in header `X-Service-Key`

Calculate astronomical gravitational forcing potential (spring/neap, perigee, etc) for a specific location.

## Query parameters

- `lat` number, required: Observer latitude
- `lon` number, required: Observer longitude
- `date` string, nullable

## Response `200`

Tidal forcing metrics and indices

- TidalForcingResponse: Full tidal forcing analysis for a location and time.
  - `date` string, required: Date in YYYY-MM-DD format (if requested by date)
  - `equilibrium` EquilibriumTide, required
    - `combined_m` number, required: Combined equilibrium tide (meters)
    - `lunar_component_m` number, required: Lunar component of equilibrium tide (meters)
    - `note` string, required: Explanatory note
    - `solar_component_m` number, required: Solar component of equilibrium tide (meters)
  - `forcing_indices` ForcingIndices, required
    - `diurnal_class` string, required: Tidal regime classification
    - `diurnal_inequality` number, required: Diurnal inequality value
    - `king_tide_risk` number, required: King tide risk score (0 to 1)
    - `perigee_proximity` number, required: Perigee proximity score (0 to 1)
    - `spring_neap_index` number, required: Spring-neap index (-1 to +1)
    - `syzygy_status` string, required: Syzygy status
    - `total_forcing` number, required: Total tidal forcing score
  - `julian_day` number, double, required: Julian Day of the calculation
  - `lunar` TidalLunarData, required
    - `days_to_perigee` integer, required: Approximate days to next perigee (-1 if unknown)
    - `declination` number, required: Moon declination in degrees
    - `distance_anomaly` number, required: Distance anomaly (perigee proximity)
    - `distance_km` number, required: Moon distance in km
    - `perigee_status` string, required: 'near_perigee', 'near_apogee', or 'intermediate'
    - `phase_angle` number, required: Lunar phase angle in degrees
    - `phase_name` string, required: Lunar phase name
  - `meta` TidalMeta, required
    - `calculation_ms` integer, required: Calculation time in milliseconds
    - `calculation_type` string, required: Type of calculation performed
    - `disclaimer` string, required: Disclaimer about astronomical vs local predictions
    - `ephemeris` string, required: Ephemeris used, e.g., 'DE440'
  - `observer` Observer, required
    - `lat` number, required: Observer latitude
    - `lon` number, required: Observer longitude
  - `solar` TidalSolarData, required
    - `declination` number, required: Sun declination in degrees
    - `distance_au` number, required: Sun distance in AU

## Other responses

- `400`: Bad Request
- `422`: Validation Error
- `500`: Internal Server Error

---

[API](https://skmtc.dev/openephemeris/apis/open-ephemeris-api.md) · [All operations](https://skmtc.dev/openephemeris/apis/open-ephemeris-api/llms.txt) · [OpenAPI document](https://skmtc.dev/openephemeris/apis/open-ephemeris-api/revisions/d195a769cb89?raw)