Purty, aren't they? I looked up the definition on Wikipedia: Crepuscular rays, are rays of sunlight that appear to radiate from a single point in the sky. These rays, which stream through gaps in clouds or between other objects, are diverging columns of sunlit air separated by darker cloud-shadowed regions. The name comes from their frequent occurrences during crepuscular hours (those being dawn and dusk), when the contrasts between light and dark are the most obvious. Various airborne compounds scatter the sunlight and make these rays visible, due to diffraction, reflection, and scattering.
When I was growing up, I thought Angels rode the rays from heaven down to Earth and back. This image was taken looking West down my street during the early evening (5:40 PM).