Time Conversion

Delta T (TT-UT1) calculation

Provide Delta T (TT - UT1) for any historical/future epoch.

get/time/delta-t

Request

  • Base URL: https://api.openephemeris.com
  • URL: https://api.openephemeris.com/time/delta-t
  • 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

Query parameters

datestring required

Date (YYYY-MM-DD)

Example:2026-03-15

Headers

authorizationstring nullable
X-API-Keystring nullable
X-OpenEphemeris-API-Keystring nullable
apikeystring nullable

Response

Successful Response

datestring required

Date string used for calculation

delta_tobject required

Delta T value (seconds) and its components

julian_daynumber double required

Julian Day for which Delta T was calculated

modelstring required

The mathematical model used (e.g., Stephenson 2021)

uncertaintyobject required

Estimated uncertainty in the Delta T value

Changes

No recorded changes to this operation across all 1 revision of this API.