All That Glitters

Living on an island has many advantages, especially for one who revels in observing natural colour and light patterns. Light reflected off water provides such a great variety of phenomena to enjoy, and here they are, all around me.

Glitter from evening sun One of my clear-sky favourites is glitter, particularly the sun glitter formed when the solar orb nears the western horizon. (It is as glorious in the post-dawn hours but, although I am usually up at that time, I am rarely about.

During those last minutes of daylight, the extra-long atmospheric path the sun's rays must traverse removes — via scattering — most of the blue-spectral light. Thus, the western sky is bathed in a mixture of reds, oranges and yellows that would fill an artist's pallet: crimson, salmon, gold, pumpkin, rose. The solar orb itself bursts forth in vivid reds and oranges, depending on the clarity of the air along its path.

When we stand facing the setting sun and look across an expanse of water, the sun's reflection paints an elongated brilliant trail of light on the sea. This is glitter. When the sun is low, the glitter trail extends from the horizon toward us, terminating at the water's edge, or very close to us if we are near shore or off shore. Once the sun reaches the horizon, however, glitter vanishes.

Glitter is not a single entity, but the composite of innumerable sun glints. Each glint is formed by a reflected solar ray emanating from a portion of the water's surface seated with the right slope and position to send the light to our eyes.

The glitter pattern we see on that trail is banded and ever altering as the restless sea surface presents a new set of reflecting cells each moment. And as when viewing the rainbow, side-by-side observers enjoy their own unique glitter pattern.

Sun Glitter from Space, courtesy NASA
Sun glitter from space,
Photo courtesy NASA.
The glitter trail is actually a very elongated ellipse as is evident when the pattern is viewed from aloft. The width and height of the glitter trail ellipse vary with the altitude of the sun and the wave pattern development. The height of the glitter pattern (as measured in degrees of view angle) always exceeds the width. When the sun is high in the sky, the height is four times the maximum wave inclination angle (denoted by a in the accompanying diagram, and the width is calculated by multiplying the height by the sine of the solar altitude angle. Therefore, the width is always narrower than the height, except in the special case when the sun is overhead and the pattern is circular.

When we view this ellipse from close to the surface, however, it becomes very much elongated, the more slanting the view angle, the longer and narrower the glitter trail.

When the solar altitude equals twice the maximum wave inclination, the glitter trail reaches to the horizon, its maximum vertical extent. As the sun sinks further, the height begins to decrease so that by the time it reaches the horizon and its altitude becomes less than the maximum wave tilt, waves may shadow others in the wave field. Thus, the glitter decreases in vertical extent and loses some brightness, eventually disappearing, leaving only scattered glint of the highest wave crests.

Since glitter is formed by reflected light, the path takes the colour of the sun. This forms those brilliantly coloured glitter path so commonly seen in photographs and film. All that glitters may not be gold, sometimes it's orange or crimson or salmon or...

Learn More From These Relevant Books
Chosen by The Weather Doctor

Lynch, David K. and Livingston, William: Color and Light in Nature, 2nd edition reprint, 2010, Thule Scientific; (PB).
Dunlop, Storm: The Weather Identification Handbook: The Ultimate Guide for Weather Watchers,, 2003, The Lyons Press, ISBN 1585748579. (pb).

Written by
Keith C. Heidorn, PhD, THE WEATHER DOCTOR,
June 15, 2002