  Time scales consistently provide precise time stamps and time intervals by
combining atomic frequency standards with a reliable local oscillator. Optical
frequency standards, however, have not been applied to the generation of time
scales, although they provide superb accuracy and stability these days. Here,
by steering an oscillator frequency based on the intermittent operation of a
$^{87}$Sr optical lattice clock, we realized an "optically steered" time scale
TA(Sr) that was continuously generated for half a year. The resultant time
scale was as stable as International Atomic Time (TAI) with its accuracy at the
$10^{-16}$ level. We also compared the time scale with TT(BIPM16). TT(BIPM) is
computed in deferred time each January based on a weighted average of the
evaluations of the frequency of TAI using primary and secondary frequency
standards. The variation of the time difference TA(Sr) $-$ TT(BIPM16) was 0.79
ns after 5 months, suggesting the compatibility of using optical clocks for
time scale generation. The steady signal also demonstrated the capability to
evaluate one-month mean scale intervals of TAI over all six months with
comparable uncertainties to those of primary frequency standards (PFSs).
