a paper delivered to the
Oregon Chapter of the
American Association of Physics Teachers
April 25, 1992
by P. R. Pennington
 

Venus is visible in the daylight.  It's very bright and easy to see even when fairly close to the sun.  I had set up stakes in the ground to help me find it at several specific times during the afternoon: I would stand at a stake appropriate for the hour and sight along the corner of the high dormer on the house.  There would be Venus.

Without the sighting aids it was much harder to find.  You can be looking right at it and still not see it.  Then, "pop," something changes  in the way you are perceiving, and there it is, glaringly obvious.  So I tried to estimate where it would be in the morning and looked there.  No house corners were there to sight over; just a big expanse of clear sky.

I couldn't find it.  But I did find a big piece of paper that had been picked up by the gusty winds and was randomly floating about, very high up.  It looked a lot like the big weather balloons I had watched floating up over military air bases during World War II.  They were aluminized and shone brightly as they moved in the upper winds.  No Venus.

In the early afternoon, I took up position at my first stake and sighted over the house corner.  There was the piece of paper!

The piece of paper was Venus.  It had been Venus all along.  Its random motions were all in my head, an illusion of staring up high into a large expanse of sky.  And then I realized that I had never followed the path of a large aluminized weather balloon.  They had been Venus every time.  They were "UCO's," Unidentified Celestial Objects.

Perception is the first window to knowledge.  Human perception is only human, and it^,s only a beginning of observation.

BEES AND SUNLIGHT
Bees see polarization of light-and it helps them navigate because a small patch of blue sky reveals where the sun is.  The direction of polarization tells the direction of the sun, and the magnitude of the polarization tells the distance to the sun.  Imagine trying to explain to Newton-or Archimedes, or King Tut, or a prehistoric artist at Lascaux cave-that bees know something about polarization of light!

Bees also see ultraviolet light, and so they see a phenomenon which is virtually unknown to humans.  Uv is greatly attenuated by Rayleigh scattering as the sun gets low in the sky.  Furthermore, the attenuation is extremely (fourth power) dependent on wavelength.  If we had visual uv detection with wavelength discrimination (color) we would see a profound shift in color as the sun changes height in the sky.  With the sun greater than 40^o - 50^o from the zenith much of the uv is largely gone.

We actually do have a perception of uv of a sort: sunburn.  But we don't have the information processing to go with this radiation detection that we need to use it effectively.  So a common error goes something like the TV weatherman's comment: "Take your sunscreen if you^'re going to Mt Hood today: it's going to get up to 70^o there today."  "Today" was December 26.  There was essentially no uv, even at noon.  Nobody got sunburned.  Nobody noticed that nobody got sunburned.  Nobody noticed that temperature is irrelevant to causing sunburn-it correlates, but correlation is not causation.  Nobody noticed that an error was made in anticipating the outcome of the exposure to the sun.  Many "obvious" things went unobserved.

For many years, Arizona newspapers have published uv intensity data.  These data clearly show the sun-angle dependence.  The sun-angle dependence is virtually never noticed.  Nor are the several oddities about the data: the person in Tucson who actually reads the uv meter, when asked, reported that she does not understand just how the system works or how to resolve the difficulties created by such descriptions as a "546-minute exposure . . . during the hour ending at 9 am."  The astronomer (at U of Ariz) who she said had set up the system, when asked, reported that he, too, had wondered about those strange numbers-he had not set up the system and had no idea who had.  The trail got cold and was pursued no further.  The obvious ambiguities and discrepancies in the daily "Sun Intensity" data go largely unobserved by the million or so people who see them daily.  The irrelevance of temperature goes largely unobserved; the relevance of sun angle goes largely unobserved.
 

SUN ANGLE (deg) 19-Nov (solar noon = 12:09) 9am    69.0 10am  54.7 11am  54.7 12       52.1 1pm    53.5 2pm    58.4 3pm    66.2 4pm    75.9 Sun angles from the zenith, for Tucson, AZ, where the instrument used is located.

SUN ANGLE (deg) 11-Jul (solar noon = 12:29) 9am   47.1 10am  34.5 11am  22.2 12       11.9 1pm    12.0 2pm    22.5 3pm    34.8 4pm    47.5 Table printed in many Arizona newspapers.