src/Marando/AstroDate/AstroDate.php
public function toTT()
    {
        if ($this->timescale == TimeScale::TT()) {
            return $this;
        }

        $this->toTAI();

        $tai1 = $this->jd;
        $tai2 = $this->dayFrac;
        IAU::Taitt($tai1, $tai2, $tt1, $tt2);

        $this->jd        = $tt1;
        $this->dayFrac   = $tt2;
        $this->timescale = TimeScale::TT();

        return $this;
    }
public function toTT()
    {
        if ($this->timescale == TimeScale::TT()) {
            return $this;
        }

        $this->toTAI();

        $tai1 = $this->jd;
        $tai2 = $this->dayFrac;
        IAU::Taitt($tai1, $tai2, $tt1, $tt2);

        $this->jd        = $tt1;
        $this->dayFrac   = $tt2;
        $this->timescale = TimeScale::TT();

        return $this;
    }
Converts this instance to Terrestrial Dynamic Time (TT)

@return static