Sometimes around sunrise or sunset, when clouds on the horizon block the sun but the
sky overhead remains clear, dark bands curve across the sky. Known as crepuscular rays,
they are the shadows formed by cloud tops, and separated by strips of light still lit by
the sun. The shadows may also be caused by mountains or clouds already below the horizon.
At these times, the bands resemble ghostly fingers.
Sometimes these rays stretch from one horizon to the other, appearing far apart when
they are directly overhead, then coming together again opposite the sun. The rays are
actually parallel throughout their entire course, but it is a trick of perspective that
makes us think otherwise.