I think 30 comes from the Synodic month - the time from first crescent to first crescent of the moon, which varies between 29.18 and 29.93 days. There of 12 of

I think 30 comes from the Synodic month - the time from first crescent to first crescent of the moon, which varies between 29.18 and 29.93 days. There of 12 of these months within a year (and a few days left over).