"And it is He who created the night and the day and the sun and the moon; all [heavenly bodies] in an orbit are swimming," meaning: they run. Al-Hasan's interpretation: The sun, the moon, and the stars are in a mill between the heaven and the earth, like the whorl of a spindle in which they rotate; and were they attached to the heaven, they would not run.
﴿وَهُوَ الَّذِي خَلَقَ اللَّيْلَ وَالنَّهَارَ وَالشَّمْسَ وَالْقَمَرَ كُلٌّ فِي فَلَكٍ يسبحون﴾ أَي: يجرونَ، تفسيرالحسن: إِنَّ الشَّمْسَ وَالْقَمَرَ وَالنُّجُومَ فِي طَاحُونَةٍ بَيْنَ السَّمَاءِ وَالْأَرْضِ كَهَيْئَةِ فَلَكَةِ الْمِغْزَلِ تَدُورُ فِيهَا، وَلَوْ كَانَتْ مُلْتَزِقَةٌ بِالسَّمَاءِ لَمْ تَجْرِ.
