Road Bow

Road Bow pictured by Abudulla Saheem (photostream). ©Abudulla Saheem, shown with permission.

The broad bow centered on the antisolar point marked by the shadow of Abudulla's head is produced by small beads of glass at the surface of the bricks.

Glass refracts light strongly and produces a primary rainbow only 21 degrees or so in radius. The Descartes diagram at right shows the ray paths.

The bow width depends on the sphericity and size of the beads

In contrast to glass, water refracts more weakly and produces the huge and familiar rainbow of ~42° radius.

Large dewdrops on the ground produce a water bow. How do we know that this one was not produced by water drops?

The field of view or focal length of Abudulla's 'phone camera is unknown. Sony Ericsson stated "the information that you are requesting is something that we are unable to provide to end users". However, it seems that most mobile 'phones cameras have a field of view of 50-70°. A water bow of 84° diameter would more than fill the frame. Abudulla also notes that the image was taken "on a clear blue morning at a dry car park. There was no water in the air or on the ground. "

More glass bead bows (1,2).