When light encounters a strong magical field it loses all sense of urgency. It slows right down. And on the Discworld the magic was embarrassingly strong, which meant that the soft yellow light of dawn flowed over the sleeping landscape like the caress of a gentle lover or, as some would have it, like golden syrup.
The turtle moves!
You’re saying it’s a relativistic effect?
https://www.terrypratchettbooks.com/read-an-extract-from-the-light-fantastic/