Physics Photo of the Week

December 20, 2013

Frosty Leaves
"Frosty" is not about to leave anytime soon, 1 day before the winter Solstice on Dec. 21, 2013.  "Frosty" left its imprints on the edges of many leaves yesterday when the temperature dropped to about 20 deg F overnight and the humidity was low enough not to form an overwhelming coating of frost, but just the right amount to form a delicate outline on the edges of each leaf on my neighbor's ground cover.  Click on the image for a larger photo.

For frost to form (or dew, rain, mist, or snow) the water vapor in the air requires a nucleation site - a speck of dust, sharp edge, or a pointed surface.  The sharp edges or surfaces of impurities provide microscopic bonding sites that attract the vapor molecules from the air to form droplets - or crystals if the condensation temperature ("dew point") is below the freezing temperature of the vapor.  Thus the frost tends to form around the edges of the objects giving the fringe on each leaf.  On the leaf in the center of the photo even the ridges of veins in the leaf accent the frosty outline of the vein pattern in the leaf.  The formation of frost crystals directly from the air, without going through the liquid water stage, is called sublimation

I am very grateful to my wife Vicki for finding and suggesting this photo on a recent early morning walk.  Other frost photos can be seen in Physics Photo of the Week for Dec. 14, 2012, and Feb. 24, 2012

This is the last Physics Photo of the Week for 2013 before Warren Wilson College closes for the Christmas Holidays.  The next Physics Photo of the Week will be posted on Jan. 24, 2014 with the 10th anniversary of Physics Photo of the Week!  Have a very Merry Christmas!

Physics Photo of the Week is published weekly during the academic year on Fridays by the Warren Wilson College Physics Department. These photos feature interesting phenomena in the world around us.  Students, faculty, and others are invited to submit digital (or film) photographs for publication and explanation. Atmospheric phenomena are especially welcome. Please send any photos to

All photos and discussions are copyright by Donald Collins or by the person credited for the photo and/or discussion.  These photos and discussions may be used for private individual use or educational use.  Any commercial use without written permission of the photoprovider is forbidden.

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