Within narration in past tense, should a statement of a universally true fact be in past tense or in present tense? For example, in the short text:
It was late afternoon in Zubrin. The air was perfect and the breeze was light. The sky glowed with the brilliance of Saturn's exotic face, a face that hung almost directly overhead and moved very little. This was due to the fact that, like Earth's moon, Titan's rotation is synchronous in its orbit. One side always faces the planet. It was a spectacular sight when the climate shield was high.
Is "is synchronous" correct, or should it be "was synchronous"? And then, "one side always faces" or "one side always faced" the planet.