Physics Photo of the Week
Needles from the sky
January 10 this winter - during one of the major snowstorms - it was
very cold with a light snow falling. This snow was unusual for
ground-reaching snow in that the snowflakes were tiny needles.
One snowstar is visible in this photo.
A fine dusting of snow lay on the vinyl grill cover, the mesh pattern
is aout a 2 mm in size. These snow needles are thus
about 3 mm long and about 0.1 to 0.2 mm across. A close-up photo
of a cluster of shorter needles is shown below.
These snow needles are not nearly as spectacular as snow stars (see
PPOW for January 22, 2010). However, these needle-like
crystals are important in producing wonderful optical effects in the
atmosphere when they form at high elevations in some cirrus
clouds. Because of the hexagonal nature of ice, these snow
needles are believed to have hexagonal cross-sections resembling
hexagonal wooden pencils. When they fall they tend to line-up
with the long axes horizontal. Light from the Sun or Moon shining
through these crystals creates the spectacular Solar and Lunar 22
degree haloes (see
PPOW for December 3, 2010).
To produce the close-up photos without an expensive macro lens, I
handhold a fairly powerful magnifier up to the camera lens and take the
photo. It is rather difficult to hold the lens centered on the
camera lens without scratching the surface in addition to keeping the
optics in focus. I used a "paparozzi" mode - snapping a
continuous stream of images while slowly moving the camera-subject
distance to have a better chance of capturing an in-focus image.
Photo of the
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 firstname.lastname@example.org.
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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