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Science Frontiers ONLINE No. 95: Sep-Oct 1994 |
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Sylvanshine: a newly recognized optical phenomenon
Driving along a forested British Columbia road on a warm August night, A.B. Fraser noticed that some trees in the dark woods glowed spectacularly in the car's headlights -- almost as if they were covered with snow. Obviously snow was out of the question. Instead, the glow was some form of reflection from dew-covered leaves, and only from certain species of trees at that.
"Later nocturnal expeditions with a powerful flashlight (a proceeding that aroused dark suspicions in at least one local gamekeeper) showed that it favoured only certain types of conifer and a few shrubs such as the yew and rhododendron. The explanation lies in the contact angle of the droplets on the leaves: as this rises above 90 degrees or so, the proportion of light from the car's headlamps that is reflected back towards the occupant increases, and for angles above 140 degrees, the retroreflection becomes spectacular. Blue spruces show the glow particularly well."
(Matthews, Lindsay; "Reflections on a Summer's Night," Nature, 369:441, 1994.)