When looking at the sun through the frost patterns on the windshield of my car on May 4, 2014, I saw a well-defined yellow and red corona. The ice crystals on the window pane worked as an obstacle which diffracted the light, which means they deviated it into different directions. So the light waves can reach areas which are blocked out when following the direct way. A diffraction pattern always consists of bright and dark spaces. The dark spaces are those where waves extinct each other, while the bright areas are at the positions where the light waves add each other. Coronae which are really circle-shaped form in grids with periodical gaps as for example in fabric. Irregularly collocated diffracting particles, however, form coronae which change their shape significantly when seen from different angles (1–2).
Author: Claudia Hinz