Wednesday, April 9, 2014

Moon reflections on the calm sea

Peder Krøyer, Summer evening on Skagen's beach, 1899
In this painting by Peder Krøyer, moonlight is reflected on the calm sea. The highlights extend vertically downward. They skip some areas altogether, but become a bright streak where the water is calm, horizontal strokes where the water is roughened by wind. They form an S-shaped squiggle on one wavetop.

The highlight turns to the side when it climbs the inclined surface of the wet sandy beach. The same thing would happen if you held a mirror at that angle.

In Sir Montagu Pollock's 1903 classic book Light and Water: A Study of Reflexion and Colour in River, Lake, and Sea, he explains how the varied wavelets act like mirrors pointing slightly toward or away from the viewer, thus stretching the moon's reflection downward.

He lays out the following general rule: "In the rippled water the combined effect of all the images of the luminous point P, formed by the reflexions in countless wavelets, is a vertical line of light."

Pollock makes another observation about the sun or moon's reflection on calm water:
"The width of this streak of light also depends largely upon the height of the sun or moon above the horizon. As the sun mounts in the sky it gets wider and vaguer."
Thanks, Tim Atkins for the Kroyer photo!
Download Pollock's book for free on
More about water, light, and reflections in my book: Color and Light: A Guide for the Realist Painter


Tom Hart said...

Very interesting and informative post, as always. It keeps me thinking about the Alma Tadema post a couple of days ago. I can't seem to get that one out of my mind. Anyway, this post points out that artists have observed water and reflections accurately for...well, for centuries. Alma Tadema was as skilled an observer as any. This leads me to the suspicion that the water in that bath didn't really "look right" to him - except in the sense that it was a conscious choice to alter realism for the sake of the image.

Artist Joseph Morris said...

An observation I made is that all reflections, be it the sun, moon or street lights, always end at your feet.

Dan said...
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