In Surah Ya-Sin (36:39), the Quran declares: "And the moon - We have determined for it phases, until it returns [appearing] like the old date stalk."
This verse describes the phases of the moon and its final form at the end of the lunar cycle, comparing it to a withered, curved old palm stalk.
The image of the "old date stalk" (ourjoun al-qadim) is of remarkable astronomical precision. At the end of the lunar cycle, the moon appears as a thin curved crescent, whose shape precisely evokes the stalk of the date palm that curves and dries with age.
Modern science has confirmed that the moon follows a precise cycle of phases: new moon, first crescent, first quarter, full moon, last quarter, last crescent, then return to the new moon. This cycle lasts about 29.5 days.
The verse also mentions that these phases are "determined" (qaddarnahu), which corresponds to the notion of precise calculation of lunar positions, confirmed by modern astronomy.
The lunar calendar, based on these phases, has been used for millennia and remains the official calendar of Islam. The precision of the Quranic description of lunar phases, made 1400 years ago, is a remarkable testimony to the concordance between the Quran and science.