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 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 40o - 50o 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 70o 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.

(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.

(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.


Uranus was discovered by Herschel in 1781, after many millennia of being unobserved.  Nevertheless, Uranus, and the asteroids Ceres (discovered 1801) and Vesta, are naked eye objects easily seen in a cloudless, moonless night sky as rather bright objects, moving in "planetary" (wandering) paths.

The outer planets are relatively stationary, and the earth moves sufficiently in a night or two that taking photos of those outer planets a night or two apart produces stereo pairs of the outer solar system.  Even Neptune is easily visible on a 15-minute exposure (tracked with a simple tracker) at f/1.4.  Stereo pairs stereoscopically showing Saturn, Uranus, Neptune and Vesta, all in or near Sagittarius, were made (July, 1989).

During the first weeks of January, the drive home from work in the evening is with a great deal more sunlight than had been present only a month earlier.  However, the drive to work in the morning is about the darkest of the year.  The earliest sunset is not on the winter solstice: it's on about December 9.  The latest sunrise is on about January 2.  Even if you don't notice the light and dark of driving to and from work, you should notice the peculiarities in the sunrise and sunset times given by TV weather persons.  This "obvious" peculiarity goes virtually unobserved.  (You can see this oddity in the graphs on this page: to Explore Portland.)

It's not to be lightly dismissed.  (One TV weatherman thought it was due to refraction of sunlight by the Earth's atmosphere.  Symmetry considerations make that "obviously" wrong.)  A little thought shows that it's a lot more interesting.  Between December 9 and January 2, both sunrise and sunset are getting later.  So, the time halfway between, which is very nearly solar noon, is getting later.  That means that the length of the day-quite reasonably defined as the time from one solar noon to the next solar noon-is changing.  Now that is interesting!

Two major factors influence length of day: angular velocity of the earth's spin and orbital velocity about the sun.  Our modern digital watches can be used to establish that spin is not varying significantly.  So it's orbital speed that must be varying.  Kepler and Newton took this observation a long way-but arrived at their profound results from other "obvious yet unobserved" phenomena.  (They didn't have digital watches, daily TV weather reports, or cars to drive to and from work under the timing of WWV signals.)

Those TV weather reports daily report the average and record temperatures.  The record lows for Portland, Oregon show a remarkable phenomenon that is virtually unobserved, even by the weather persons.  Graphing the records shows it clearly.  (Extreme lows in Portland are caused by drives of arctic air that get pushed unusually far south.  These air masses continue to get colder as the arctic night progresses.  The two major factors are, probably, the ending of the arctic night and the cutting off of those north to south drives of air.)

Collect, and study, those "obvious yet unobserved" phenomena!  They teach a lot.