SolarEclipses.com

Delta-T Calculator

Choose a solar eclipse or enter a date and time in UTC, UT1, or TT, then Calculate.

Selecting an eclipse loads its greatest-eclipse TT epoch.
Uses this computer's system clock and enters the instant as UTC.
Time scale:
ΔT = — s
DUT1 = — s
Source will appear here

About this calculator

This calculator returns ΔT = TT − UT1 and DUT1 = UT1 − UTC for dates from 1900 through 2200.

Every result is color-coded by its source. Gray values use IERS historical Earth-orientation data, green values use IERS calculated Earth-orientation data, blue values use active IERS predictions, and red values use a named long-range ΔT model when the requested date lies beyond the IERS prediction range. The exact IERS series or prediction/model used is shown with the result.

Modern values are derived from Earth-rotation data and interpolated to the requested instant. The method and data page documents the equations, source files, interpolation procedure, update process, and enough information to reproduce the calculation independently.

Method & data documentation →