Rainbows Above Vajont Dam, Italy

June 29, 2016


Photographers: Pictores Caeli: Dario Giannobile, Giorgia Hofer, Marco Meniero, Marcella Giulia Pace
Summary AuthorsPictores Caeli Team; Jim Foster

It's sometimes easy to misinterpret optical phenomena, especially if a long focus lens is used or if the perspective is unexpected. The photo above is such an example. The colors and color repetition appear to be some sort of corona, but what we're actually seeing is a rainbow. In fact, we see parts of two primary rainbows; the top portion of a normal rainbow and a reflected rainbow -- likely reflected from the water impounded by the dam at the bottom. The Sun was evidently near the horizon when the photo was snapped.

In essence, the Sun has reflected off smooth lake water, and the upward going reflected rays have formed a second rainbow that's centered on a point the same distance above the horizon as the Sun. The normal primary rainbow is centered on the antisolar point below the horizon. If the photo had been taken at exactly sunset, these two points and their corresponding rainbows would have overlapped. However, since it was taken shortly before sunset, the two bows are just slightly separated. Photo taken on May 2, 2016, at Vajont Dam in Italy. To learn more about rainbows see Les Cowley's Atmospheric Optics.

Photo Details: Camera Model: NIKON D750; Lens: 24-120mm ƒ/4-4; Focal Length: 120mm (35mm equivalent: 120mm); Aperture: ƒ/7.1; Exposure Time: 0.0010 s (1/1000); ISO equiv: 250; Software: Adobe Photoshop CC 2014 (Macintosh).