الشَّمْسُ وَالْقَمَرُ بِحُسْبَانٍ
The sun and the moon follow a determined reckoning.
The two celestial bodies are appropriately joined through their ordered motions and association with the reckoning of time. The phrase bi-ḥusbān reinforces the shared idea of measure and regularity.
The merit is not simply the juxtaposition of two astronomical names. They have been selected to form a coherent picture of cosmic order, although neither term is a synonym or explanation of the other.