  The Black Hole Explorer (BHEX), an orbiting, multi-band, millimeter
radio-telescope, in hybrid combination with millimeter terrestrial
radio-telescopes, is designed to discover and measure the thin photon ring
around the supermassive black holes M87* and Sgr A*. As background to the BHEX
instruments, this paper explores various aspects of the photon ring, focusing
on the intricate flow of light around a spinning black hole, and tracking,
through visual simulations, photons as they course along geodesics. Ultimately,
the aim of these visualizations is to advance the foundational aims of the BHEX
instrument, and through this experiment to articulate spacetime geometry via
the photon ring.
