Function: deltaTSigma()
function deltaTSigma(year): number;
One-sigma uncertainty of delta T (TT - UT1) in seconds at a calendar year.
Breakpoints from Morrison & Stephenson, "Historical values of the Earth's clock error deltaT and the calculation of eclipses" (J. Hist. Astron. 35, 2004), Table 1's sigma column; the telescopic era tapers to the IERS measured span (effectively exact), and the future grows quadratically from the end of the measured tables (extrapolation, stated as such). Linear interpolation between breakpoints.
This is what bounds ancient charts: at year 150 the position theories are fine but sigma(deltaT) is minutes, which smears the fast movers -- the Ascendant/MC rotate 0.25 deg per minute of clock error and the Moon moves 0.55 arcsec per second -- while Jupiter barely notices. Chart warnings report exactly that split.
Parameters
| Parameter | Type |
|---|---|
year | number |
Returns
number