Physics Photo of the Week
Tunnel spiders are very common in the late summer.
These spiders spin matted webs on vegetation near the ground. The
spider's lair is at the end of a tunnel woven in the sheet.
These layers of sticky silk presumably serve to catch insects similar
to the spoke and spiral spider webs we are familiar with. These
traps apparently use much more silk.
The tunnel spider traps/nests show up very clearly in the morning as
they accumulate much dew. If the Sun is at the correct angle, a
rainbow of colors is quite noticeable. The rainbow effect is
caused by the myriads of dew drops that have collected on the web
fibers. The fibers
dew drops are so small that the drops are spherical - the same
requirement for a typical rainbow (see PPOW,
4, 2008 for a rain rainbow and explanation). The photo
at right shows the whole web for the tunnel spider. The dew
droplets on the silk
fibers are not resolvable, but one still sees the rainbow
colors as in the close-up photo above.
When examining these rainbow colors in the dew, if one moves one's eyes
slightly to one side, one is no longer at the optimum position to see
spectral colors. The photo below shows the same tunnel spider's
web, but from a slightly different angle. No colors are seen.
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
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explanation. Atmospheric phenomena are especially welcome.
Please send any photos to firstname.lastname@example.org.
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