In this 16mm film, Tacita Dean shows us the green ray, the slowest setting ray of light just before the sun disappears on the horizon. The artist was able to capture this elusive phenomenon using celluloid film, in her conviction that this format offers the possibility to see something that digital cameras cannot. Dean has devoted much of her practice to advocating for the permanence of analog film technology in the future, not instead but alongside digital formats, as the comparison between the images each medium produce offers insights into our perception of the world around us. While the green ray is caused by a combination of the dispersion, scattering, and refraction of light, the film aims to capture a moment of sublime yet fleeting experience.