I first took note of this Han Shan poem thanks to a Twitter posting by @EstherHawdon. What caught my eye was the first stanza, which struck me as unusual for Tang poetry, going beyond the typical Yin-Yang cosmology as a way of describing the workings of celestial light. But as @EstherHawdon pointed out to me, the Chinese astronomer Zhang Heng (AD 78-139) had been a very early propounder of the theory that the moon borrows its light from the sun.
In any case, notable as the first stanza is, I find the second stanza even more remarkable -- Han Shan's own unique observations about indirect illumination - how the sun lights the moon and the moon itself provides illumination for the poet's own soul.