Full Circle Rainbows

Most people know a rainbow only as a bow in semicircular shape which becomes smaller with increasing sun elevations and disappears beneath the horizon at a sun elevation of 42°. But this is only half of the truth, just as a complete rainbow is a full circle. But it is not easy to observe and photograph it in its full beauty. This is because the lower part of a rainbow can only appear when there are enough drops of water below the horizon to make it bright enough. During the last two months, both variations could be captured.

One case in which a rainbow can be seen as a full circle is when the sun shines through the spray of a waterfall. With the sun standing low behind the observer, the rainbow continues downward in front of the background, and with a little luck the full circle becomes visible. The photograph above was taken by Wolfgang Hinz on July 29, 2014 at the Seljalandsfoss-Waterfall in Iceland. More pictures: 1–2–3

But it is also possible to see the lower part of a rainbow from an airplane. During a flight on August 12, 2014, Peter Krämer could even look upon a part of a rainbow from above, whith the houses of the city of Essen behind it. But unfortunately the windows in a plane are rather small, so that a full circle rainbow can only be seen from the cockpit. But nevertheless, Peter Krämer could catch the right part of the rainbow when the pilot made a light left turn  (1–2).

The lower part of a rainbow can also be seen from a mountain. Here it is necessary that opposite the sun rain falls into a deep valley. In the morning of July 8, 2014, Claudia Hinz saw a rainbow which appeared on an approaching rain front from Mt. Zugspitze (2963m), the right part of which excended downwards until the village of Ehrwald. As the sun was just rising, the spectral colours were filtered out of the sunlight by the atmosphere due to the oblique angle in which the sunlight fell in. So the rainbow showed only a long waved red colour. The other colours appeared only a few minutes later (1–2–3).

 

Authors: Claudia Hinz, Peter Krämer, Germany

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