02 January 2011 Sunshine Trace
Hour of Day
14 13 12 11
Clouds at sun Clock-Driven Cloud Recorder 10 November 2010
F Start 9:00
; Fig. D: Digitized sunshine trace from tea can
recorder in Figure C annotated with 30-minute grid
lines. The center grid line
was aligned with solar noon
(12: 36 p.m. on Jan. 2, 2011).
Grid lines were equally
spaced from noon to sunrise and noon to sunset.
Daily sunshine times can be
found at sunrisesunset.com.
; Fig. E: Quartz analog
clock-driven recorder with
two 1mm sunlight apertures. The black paper disk
was taped to the clock’s
hour hand. Blueprint paper
was taped to the clock face
behind the black paper disk.
; Fig. F: Dual sunshine
traces made with the clock-driven sunlight recorder.
Note the interruptions in
the traces caused by clouds
blocking the sun.
than the clock face, and make a ¼" hole at its
center. Place the axis of the hour hand over
the hole, and tape the hand to the disk. Make
a 5" hole in the disk 2" from the center. This
aperture will allow sunlight to strike the blueprint paper as the black disk rotates over it.
Cut a rectangular sheet of blueprint paper
to cover the clock face’s top half. Again, do
this indoors so that no sunlight or UV light
strikes the paper. My clock face is 7¾" in
diameter, so I cut a 3½"× 5" piece of SunArt
paper, with a V-shaped notch in the bottom to
make room for the clock drive axis.
Place the blueprint paper over the clock
face and secure it with masking tape. Finally,
place the black disk over the clock face with
its taped hour hand facing up, and its sunlight
aperture aligned at a morning hour, and press
the hour hand onto the clock axis. My 3½"× 5"
sheet allowed six hours of sunlight recording,
so I set the aperture to the 9 a.m. setting.
Place the clock outside so it faces the sky
as described earlier. Retrieve it at sunset
and remove the black disk, then remove the
blueprint paper and preserve its image by
immersing it in water with a few drops of
30 Make: makezine.com/26
To make your own cyanotype paper, see the
instructions at makezine.com/go/cyanotype.
In Google Books, you can even find recipes
and methods in Herschel’s original paper.
Is the density of the blue color of a sunlight
cyanotype trace proportional to the intensity of the sun’s ultraviolet light? Finding out
could be an excellent science project. Digitize
a sunlight trace, then use photo software to
determine the blue density at uniform intervals along the trace. Compare these data with
the UV for your site measured by a Solarmeter
( solarmeter.com) or similar UV radiometer,
or by the nearest radiometer in the U.S.
Department of Agriculture’s UVB monitoring
program ( makezine.com/go/usda_uvb).
Finally, pinhole cameras can be used with
ordinary photo paper to make spectacular
sunshine traces of up to six months’ duration.
See Tarja Trygg’s how-to instructions at
www.solargraphy.com and Justin Quinnell’s
images at pinholephotography.org. ;
Forrest M. Mims III ( forrestmims.org), an amateur scientist
and Rolex Award winner, was named by Discover magazine
as one of the “ 50 Best Brains in Science.” His books have sold
more than 7 million copies.