---
title: "Sidereal Time (LAST & GMST)"
method: GET
path: "/time/sidereal"
tags: ["Time Conversion"]
---

# Sidereal Time (LAST & GMST)

`GET /time/sidereal`

## Request

- Base URL: `https://api.openephemeris.com`
- URL: `https://api.openephemeris.com/time/sidereal`
- 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`

Compute Local Apparent Sidereal Time (LAST) and Greenwich Mean Sidereal Time (GMST).

## Query parameters

- `date` string, required: Date (YYYY-MM-DD) or Julian Day (jd:2451545.0)
- `longitude` number: Observer longitude (positive East)

## Headers

- `authorization` string, nullable
- `X-API-Key` string, nullable
- `X-OpenEphemeris-API-Key` string, nullable
- `apikey` string, nullable

## Response `200`

Successful Response

- SiderealTimeResponse
  - `equation_of_equinoxes` number, required: The nutation correction in hours
  - `gmst` number, required: Greenwich Mean Sidereal Time in hours
  - `information` object, required: Metadata about the calculation engine
  - `last` number, required: Local Apparent Sidereal Time in hours
  - `longitude_used` number, required: The observer longitude used for LAST

## 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)