I had thought the formula #Meeus gives for #SiderealTime must be inaccurate due to the uneven length of the day, but then I realized that it only gives the value for Greenwich at 0 UT, which is always corrected for the Earth's rotation and thus only dependent on the Earth's position in its orbit. Which changes slowly enough that ΔT (the difference between #UniversalTime, which is non-uniform, and a uniform clock, generally #TerrestrialTime) can't have a significant effect.

If the difference really matters to you, you can use the #EarthRotationAngle, which is the current standard for #Astronomy but that seems to be a lot more involved to compute, and it requires downloading data from the #IERS.

#MathematicalAstronomy