unixtojd(time_stamp);
Here is an example.
$tt=time(); // time stamp of today.
echo "Time Stamp = $tt ";
$day_jd=unixtojd($tt);
echo "Julian Day by using unixtojd() : $day_jd ";
The output is here
Time Stamp = 1686393108
Julian Day by using unixtojd() : 2460106
Julian Day count to Unix timestamp