code: public function toUT1()
      {
          if ($this->timescale == TimeScale::UT1()) {
              return $this;
          }
  
          $this->toUTC();
  
          $utc1 = $this->jd;
          $utc2 = $this->dayFrac;
          $dut1 = IERS::jd($utc1 + $utc2)->dut1();
          IAU::Utcut1($utc1, $utc2, $dut1, $ut11, $ut12);
  
          $this->jd        = $ut11;
          $this->dayFrac   = $ut12;
          $this->timescale = TimeScale::UT1();
  
          return $this;
      }
docs: Converts this instance to Universal Time (UT1)
  
  @return static