What is Dynamic Time (ΔT)?

ΔT is the difference TD − UT. TD is uniform (atomic). UT is based on Earth's rotation.

How is ΔT estimated between 2000 and 2100?

An empirical polynomial in t = (year−2000)/100 is commonly used for predictions.

Dynamic Time (ΔT)

The difference between uniform atomic time and Earth's irregular rotation (UT).

Universal Time (UT) or Greenwich Civil Time, used in civilian life, is based on the rotation of the Earth. However, this rotation slows down unpredictably, so UT is not a uniform time. Astronomers, in need of uniform time, utilize Dynamic Time noted TD and defined by atomic clocks. The difference ΔT = TD − UT can only be deduced from observation.

Observed ΔT (1600–2000)

Approximation for 2000–2100

With t = (year − 2000) / 100
ΔT = 102 + 102·t + 25.3·t² + 0.37·(year − 2100)

Predicted values (2000–2100)

Year	ΔT (s)
2000	64.7
2025	~88
2050	~113
2100	~160