Physics Photo of the Week - 10th Anniversary!

January 31, 2014

Levitating Block Island - Photo by Aaron Keegan, WWC Class of 2005

(Click on the photo for a full-sized image)

What causes the apparent levitation of Block Island, off the coast of Rhode Island, USA?  The answer is a simple mirage called an "inferior mirage" where distant objects appear to be reflected by a warm layer of air over the water.  Aaron took these photos on January 9, 2014 near his home very close to this spot.  Being a transportation engineer he was intrigued by the apparent levitation, and he rightly suspected optical mirages.

The northeast USA had just experienced a massive cold air spell (the first of two massive freezes this January).  The air became very cold, but the high heat capacity of the ocean prevented the ocean temperature to cool as much.  Because of the relative warmth of the ocean water relative to the air, a thin layer of air just above the water surface warmer than the higher-level air.  When light from distant objects (Block Island is about 10 miles distant) strikes the warm layer of air at a grazing angle, the smaller in refractive index (due to the smaller density of warm air), causes the ray of light to be bent or refracted upwards, as if it were reflected off a mirror.  Here the mirror is the interface of warm/cold air.  If you look carefully at the trees near the left edge of the island, the tree-tops are reflected by the mirage.  The sky above the island is also reflected giving the levitating appearance.

Aaron's mirage is the first winter mirage I've seen.  Physics Photo of the Week has published summer a summer lake mirage (September 28, 2007) - complete with theory, as well as a common road mirage seen on hot summer days (September 21, 2007) - also with a theory and even an indoor "artificial" mirage (September 28, 2012).

10th Anniversary of Physics Photo of the Week!  It is fitting that WWC alumnus Aaron Keegan sent us the Block Island photo posted today.  Aaron was a student (both at Washington University in St. Louis and at Warren Wilson College earning two degrees when on a whim I started to publish an interesting Physics Photo each week the college was in session on Feb. 6, 2004.  I thank all the many readers for their support of Physics Photo of the Week and especially for those people who have sent me interesting photos that they have captured featuring physics and other natural phenomena.  I hope to keep doing this as long as I and my computer keep working.  I also thank Warren Wilson College for the support it has given me - especially to David Harper and the Computer Services Crew for their support.  See the first Physics Photo of the Week to see how it's changed.

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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