In Surah Ali-Imran (The Family of Imran), Allah designates the alternation of day and night as a major sign for people of understanding:
"Indeed, in the creation of the heavens and the earth and the alternation of the night and the day are signs for those of understanding." (Ali-Imran 3:190)
This verse, among the most famous of the Quran, invites man to meditate on the cosmic order that governs our daily existence.
The mechanism of alternation
The alternation of day and night is due to the Earth's rotation on its axis, which takes about 24 hours. This rotation, combined with the tilt of the Earth's axis (23.5 degrees), also produces the seasons.
It was only from the Copernican revolution (16th century) that humanity understood that it is the Earth that revolves around the Sun and on itself, not the reverse. Nicolaus Copernicus published his heliocentric theory in 1543, and it took decades more for it to be accepted.
The Quran, revealed in the 7th century, already evoked the regularity of this alternation as a sign of divine order, without entering into the detail of the mechanism — an approach that avoids any contradiction with later discoveries.
The Earth's rotation: a progressive discovery
The Earth's rotation on itself was demonstrated experimentally by Léon Foucault in 1851 thanks to his famous pendulum. This definitive proof confirmed that the apparent movement of the Sun and stars is due to the rotation of our planet.
The regular alternation of day and night, a phenomenon that everyone observes daily, thus rests on a precise physical mechanism that modern astronomy has entirely elucidated.
A sign for people of understanding
Verse 3:190 emphasizes that the contemplation of the cosmic order — the creation of the heavens and the earth, the alternation of day and night — leads to the recognition of the Creator. Modern science, by revealing the precision and harmony of these mechanisms, gives new depth to this invitation to reflection.