is not visible, but can only be determined by calculation. This is how the year is reckoned by those who are not People of the Book, such as the Romans, Persians, and others. Some combine both methods. This is how the year is reckoned by those among the People of the Book who have introduced alterations and changes, as the Jews and Christians do. We have discussed this at length elsewhere.

As for the week, all agree that it has no observable basis. Rather, its basis is transmitted knowledge: what the Messengers have taught—that Allah created the heavens and the earth in six days, then rose over the Throne. Allah has prescribed that the followers of the Scriptures—Muslims, Jews, and Christians—gather every week to remember and worship Him. This preserves the reckoning of the days of the week, recalling Allah’s creation of the heavens and the earth in six days and the conclusion of that on the seventh day.

Thus, names for the days of the week occur only in the languages of those who received this knowledge from the People of the Book, such as the Persians. As for the nomadic Turks, such as the Tatars and others like them, their language has no names for these days. Their basis cannot be known through observation, and these peoples have no transmitted knowledge of it, being far removed from the lands of knowledge and faith.

As for what can be known through observation, Allah, Exalted is He, says:

“They ask you about the new moons. Say, ‘They are measurements of time for people and for Hajj.’” [al-Baqarah 189]

And He, Exalted is He, says:

“Indeed, the number of months with Allah is twelve months, according to Allah’s decree, on the day He created