Quran 2:189: They (the Jews) ask you about the phases of the moon. Say, "These are signs for the people to reckon dates and fix the periods for hajj."
Imam Qurtabi recorded the following tradition under this verse in his commentary (link):
هذا مما سأل عنه اليهود وٱعترضوا به على النبيّ صلى الله عليه وسلم فقال معاذ: يا رسول الله، إن اليهود تغشانا ويكثرون مسألتنا عن الأهِلة، فما بال الهلال يبدو دقيقاً ثم يزيد حتى يستوي ويستدير، ثم ينتقص حتى يعود كما كان؟ فأنزل الله هذه الآية.
This is what the Jews asked about and objected to the Prophet. So Muadh said: O Messenger of God, the Jews come to us and ask us about the crescents, so why does the crescent appear thin, then increases until it becomes even and round, then decreases until it returns as it was? Upon that, Allah revealed this verse.
Please ponder upon it. As you can see:
- Neither there is anything scientific in this answer
- Nor it increased anything in the knowledge of those people who asked this question, as Jews had already known that the changes in the size of the moon can be used for calculating dates.
It was a golden chance for Allah/Muhammad to tell the real reasons behind the increasing and decreasing of the size of the moon so that modern science could have also testified the scientific miracle of the Quran. Alas, the Quran and Allah/Muhammad once again missed this chance.
All brainwashed Muslims, who take scientific miracles out of the Quran today, should learn their lesson from it.
Jews had to ask this question, while the SCIENTISTS had already found the real reasons for the increasing/decreasing size of the moon
In Biblical Cosmology, the earth was flat.
Nevertheless, Scientists had already found the real reasons for the increasing/decreasing size of the moon (about 900 years before Muhammad). And those reasons went completely against the Biblical cosmology of flat earth.
Greek philosophers had already found in 500 BC that the shape of the earth is not flat, but spherical (link).
Then came the Greek astronomer Aristarchus of Samos in 300 BC, who was even able to calculate the sizes of the Sun and Moon, as well as their distances from the Earth (link).
Aristarchus began with the premise that, during a half-moon, the moon forms a right triangle with the Sun and spherical Earth.
Aristarchus then used another construction based on a lunar eclipse:
Thus, there had already been a heavy debate going on between Jews and scientists about the shape of the earth before Muhammad. The Jews claimed the earth to be flat, while the scientists claimed it to be spherical.
Therefore, the Jews came to Muhammad and asked him about the reason for the increasing/decreasing size of the Moon, while Muhammad was claiming himself to be the continuation of the Biblical prophets. They thought, if Muhammad was really a true prophet, then he would prove those scientists to be wrong by giving them the correct answer.
Nevertheless, the scientific knowledge of Muhammad/Allah was even more primitive than of Jews, as Muhammad/Allah belonged to the primitive society of Arabs of the era of ignorance. And it was reflected completely in the answer, that was given by the Quran.