This is an astronomical truth, not just a poetic turn of phrase. The moon points us eternally toward the sun, whether with the curve of her bow or the fullness of her face. And when she has waxed to circular perfection, aglow in a crystal black sky, you can draw a line from her to yourself, and then continue that line onward for 93 million miles to know where the source of her light and our lives lies hidden.
In this way, geometry and poetics and science are as one, inextricably linking brightness, beauty and understanding by dark of night.
(Many thanks to C. Joybell C. for writing a blog post that made me think of this.)