(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
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
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 email@example.com.
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.