Photo of the Week
phenomenon on cold, clear winter nights is commonly called "hoar
The temperature is below freezing and the dew point, or condensation
point for water vapor in the air is also below freezing. Water
in the air condenses directly as ice on surfaces rather than condensing
as liquid. This process is also called sublimation.
Notice how the tiny crystals of ice are hexagonal in shape. The
between the crystal edges are perfect 120 degrees. The crystals
tend to form on one another, not in isolation. Once a crystal
to form on a splinter, dust, or small protrusion in the surface, the
edges of the crystal act as nucleation
for more crystals to form.
the photo is about 1 cm wide. It was made by
holding a fairly
magnifier lens up to the camera lens to take the picture. This is
analogous to looking through the magnifier with your eye to see the
small details. The photo below right is the
frosty railing where the close-up for the picture at left was taken.
crystals form in the air as opposed to surfaces, the crystals are
"floating" or falling in the air at small
speeds. Because the
free-falling crystals are un-impeded by the surface of the object they
are attached to, they often form perfectly symmetrical snowflakes with
intricate branches. The free-floating crystals or snowflakes
require a nucleation site to form. That nucleation site for snow
flakes is often a microscopic speck of dust, volcanic ash, or pollution
Watch this page for more frost photos where the frost crystals take
different shapes. A very informative discussion of frost, snow,
and ice is maintained by California Institute of Technology professor
Dr. Kenneth Libbrecht at snowcrystals.com.
Photo of the
published weekly during the academic year on Fridays by the Warren
Wilson College Physics
Department. These photos feature an 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 firstname.lastname@example.org.
here to see the Physics Photo
the Week Archive.
are invited to submit
digital photos to: