src/Marando/AstroDate/AstroDate.php
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 $this;
    }
public function toUT1()
    {
        if ($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;
    }
Converts this instance to Universal Time (UT1)

@return static