Hmm, i wouldn't call it totally arbitrary. UTC = TAI + LS, such that |UTC - UT1| < 1 second, where:
* LS are leap seconds,
* TAI is "physicist" time, based on the ticking of atomic clocks at mean sea level. The length of a second is constant.
* UT1 is "astronomer" time, the rotation angle of the Earth with respect to the quasar reference frame. The length of a second is not constant.
The Earth's rotation is slowing down, so UT1 is gradually drifting away from TAI. UTC is a pretty natural scheme to reconcile these two systems.
Hmm, i wouldn't call it totally arbitrary. UTC = TAI + LS, such that |UTC - UT1| < 1 second, where:
* LS are leap seconds,
* TAI is "physicist" time, based on the ticking of atomic clocks at mean sea level. The length of a second is constant.
* UT1 is "astronomer" time, the rotation angle of the Earth with respect to the quasar reference frame. The length of a second is not constant.
The Earth's rotation is slowing down, so UT1 is gradually drifting away from TAI. UTC is a pretty natural scheme to reconcile these two systems.