{"openapi":"3.1.0","info":{"title":"Sidereal Time API","version":"1.0.0","description":"Sidereal-time astronomy as an API, computed locally and deterministically. The gmst endpoint computes the Greenwich Mean Sidereal Time for a UT date and time, GMST = 18.697374558 + 24.06570982441908·(JD − 2451545.0) hours modulo 24, returning it in hours, degrees and hours-minutes-seconds together with the Julian Day — sidereal time tracks the stars rather than the sun and gains about three minutes and fifty-six seconds each day. The lst endpoint adds the observer's longitude to give the Local Sidereal Time, LST = GMST + longitude/15 (east positive), which equals the right ascension of any star currently crossing the local meridian. The hour-angle endpoint computes the hour angle of a celestial object, HA = LST − RA, from its right ascension and the local sidereal time (or a date, time and longitude): an hour angle of zero means the object is on the meridian at its highest point, a positive hour angle means it is west of the meridian and setting, and a negative one means it is east and rising. Dates are YYYY-MM-DD and times HH:MM:SS in UT, longitude in degrees and right ascension in hours. Everything is computed locally and deterministically, so it is instant and private. Ideal for astronomy, telescope-control, planetarium, observatory and astrophotography app developers, star-pointing and transit tools, and astronomy education. Pure local computation — no key, no third-party service, instant. Live, nothing stored. 3 endpoints. This is sidereal time; for the sun's position use a solar-position API and for sunrise and sunset times a sunrise API.","contact":{"name":"PremiumApi","url":"https://www.oanor.com/by/premiumapi"}},"servers":[{"url":"https://api.oanor.com/sidereal-api","description":"oanor gateway"}],"tags":[{"name":"Sidereal"},{"name":"Meta"}],"components":{"securitySchemes":{"oanorKey":{"type":"apiKey","in":"header","name":"x-oanor-key","description":"Get your key at https://www.oanor.com/developer/keys"}}},"security":[{"oanorKey":[]}],"paths":{"/v1/gmst":{"get":{"operationId":"get_v1_gmst","tags":["Sidereal"],"summary":"Greenwich sidereal time","description":"","parameters":[{"name":"date","in":"query","required":true,"description":"UT date (YYYY-MM-DD)","schema":{"type":"string"},"example":"2000-01-01"},{"name":"time","in":"query","required":false,"description":"UT time (HH:MM:SS)","schema":{"type":"string"},"example":"12:00:00"}],"security":[{"oanorKey":[]}],"responses":{"200":{"description":"OK","content":{"application/json":{"example":{"data":{"note":"Greenwich Mean Sidereal Time = 18.697374558 + 24.06570982441908·(JD − 2451545.0) hours, mod 24. Sidereal time tracks the stars, not the sun, gaining ~3m56s per day.","inputs":{"date":"2000-01-01","time":"12:00:00"},"gmst_hms":"18:41:50.55","gmst_hours":18.69737456,"julian_day":2451545,"gmst_degrees":280.460618},"meta":{"timestamp":"2026-06-05T11:30:26.573Z","request_id":"d501d97b-2299-473d-b33c-a339de789c48"},"status":"ok","message":"Greenwich sidereal time","success":true}}}},"401":{"description":"Missing or invalid x-oanor-key header"},"402":{"description":"Active subscription required"},"429":{"description":"Rate-limit or monthly quota reached"},"502":{"description":"Upstream did not respond"}}}},"/v1/hour-angle":{"get":{"operationId":"get_v1_hour_angle","tags":["Sidereal"],"summary":"Hour angle","description":"","parameters":[{"name":"right_ascension","in":"query","required":true,"description":"Right ascension (hours)","schema":{"type":"string"},"example":"12"},{"name":"lst","in":"query","required":false,"description":"Local sidereal time (hours)","schema":{"type":"string"},"example":"18"},{"name":"date","in":"query","required":false,"description":"Or UT date","schema":{"type":"string"}},{"name":"time","in":"query","required":false,"description":"UT time","schema":{"type":"string"}},{"name":"longitude","in":"query","required":false,"description":"Longitude (°)","schema":{"type":"string"}}],"security":[{"oanorKey":[]}],"responses":{"200":{"description":"OK","content":{"application/json":{"example":{"data":{"note":"Hour angle HA = LST − RA. HA = 0 means the object is on the local meridian (highest point); positive HA is west of the meridian, negative is east.","inputs":{"lst":18,"right_ascension":12},"position":"west of the meridian (setting)","hour_angle_hours":6,"hour_angle_degrees":90,"hour_angle_signed_hours":6},"meta":{"timestamp":"2026-06-05T11:30:26.693Z","request_id":"d5ef4164-89bd-4377-8335-676ae731e28a"},"status":"ok","message":"Hour angle","success":true}}}},"401":{"description":"Missing or invalid x-oanor-key header"},"402":{"description":"Active subscription required"},"429":{"description":"Rate-limit or monthly quota reached"},"502":{"description":"Upstream did not respond"}}}},"/v1/lst":{"get":{"operationId":"get_v1_lst","tags":["Sidereal"],"summary":"Local sidereal time","description":"","parameters":[{"name":"date","in":"query","required":true,"description":"UT date (YYYY-MM-DD)","schema":{"type":"string"},"example":"2000-01-01"},{"name":"time","in":"query","required":false,"description":"UT time (HH:MM:SS)","schema":{"type":"string"},"example":"12:00:00"},{"name":"longitude","in":"query","required":true,"description":"Longitude (°, east +)","schema":{"type":"string"},"example":"15"}],"security":[{"oanorKey":[]}],"responses":{"200":{"description":"OK","content":{"application/json":{"example":{"data":{"note":"Local Sidereal Time = GMST + longitude/15 (east positive). 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