TT is a perfectly uniform time scale used for all astronomical calculations. It doesn’t care how Earth wobbles — it ticks smoothly according to atomic time standards. TT replaced “Ephemeris Time” (ET), which was the old theoretical time used for planetary motion.
In short:
- TT = Theoretical clock time used in equations.
- It runs ahead of UTC by about 69s right now (because of accumulated leap seconds + a fixed historical offset).
- It’s tied directly to TAI (International Atomic Time) by:
- TT = TAI + 32.184 s.
- It’s what you use when computing ephemerides, orbital mechanics, or primary directions — anything needing uniform seconds.
Summary
Functions
TT runs ahead of UTC by two parts:
- The historical offset of 32.184 s (fixed).
- The TAI–UTC offset (total leap seconds) valid at that epoch.
"TAI" = International Atomic Time
Convert a TT DateTime back to UTC.
Implementation notes:
- TT = TAI + 32.184s
- TAI = UTC + (TAI-UTC leap offset at UTC)
- We resolve the leap offset with a short fixed-point iteration (max 2 passes).