Jenny Harris, of Balclutha Primary School, asks :-

How does this Sun effect happen? It lasted only 2 minutes.

Esther Haines, a physicist at the University of Otago, responded.

The photograph shows sunlight streaming through trees shortly after sunrise. The shafts of light are examples of crepuscular rays, named from the Latin word for twilight (crepusculum) as they are often seen at sunrise or sunset.

Crepuscular rays are formed when there is an obstacle in front of the Sun that has gaps in it, for example, gaps between clouds, mountains, or leaves. This divides the air into regions that are sunlit and regions that are in shadow. For us to see the sunlit regions there must be something in the air such as dust particles or small water droplets that scatter the light so that it reaches our eyes or the camera lens. It is possible that in this case it is very small droplets of water (a fine mist) formed in cool air above ground that has cooled by radiating heat to a clear night sky. This would explain why the effect was short-lived as the droplets would evaporate as the sum warmed the air. With nothing scattering the light the effect would disappear.

The shafts of light are yellow because at sunrise the light travels a long way through the atmosphere and air scatters blue light more than other colours. Hence blue light has been removed from the sunlight, leaving red and green light, which makes yellow light.

Crepuscular rays are parallel but appear to spread out from the Sun. This is an effect of perspective, just like railway tracks appear to be getting closer the further away they are.

Crepuscular rays in the form of sunlight streaming from behind clouds are sometimes called Ropes of Maui after the story of how Maui and his brothers trapped the Sun with ropes and persuaded him to slow down so that the people had enough time in the day to complete all their tasks.