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Re: Private Universe and the Seasons - Correction & Comments - PART 1



PART 1
In my previous post "Re: Private Universe and the Seasons" (Hake
2003a) I listed some critical aspects of Seasons that are not all
adequately addressed in middle-school texts. One of these was:

"d. The Sun's rays leave the Sun nearly radially but are nearly
parallel to one another when they reach the Earth [as stressed by
Larry Woolf (2003a,b)]."

In a recent Phys-L post, Woolf (2003c) pointed out that the above
attribution is misleading - I apologize. Contrary to that
attribution, Woolf (2003a) actually wrote:

WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW
In addition, few texts address any of the following issues:
1. Why are the sun's rays parallel at the earth?
2. How do the sun's rays look when they leave the sun?
3. Why the sun's rays are shown in a radial fashion leaving the sun, then
are parallel at the earth; and why the radial diagram is also a
simplification.
4. Why the sun's rays are not really parallel at the earth, but that the
parallel nature is a useful simplification.
5. What is meant by a ray of the sun - what is it a model for?
6. Why the earth doesn't just keep getting hotter because it is heated by
the sun? - cooling mechanisms are never discussed so energy
conservation is
generally put on hold when discussing the seasons.
WWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWWW

Larry goes on to state that he is developing a poster that addresses
these issues, in a similar vein to others that he has done
<http://www.sci-ed-ga.org/modules/materialscience/color/materials.html>.

In addition to Larry's poster, other resources that might be helpful
in explaining the Seasons (some of them supplied by contributors to
this thread) are: Gould et al. (2000), Hake (2003b), Morrow & Zawaski
(2000), and SAO (1998).

In regard to the above middle-school textbook deficiencies [for a
review see Hubisz 2003], Larry quotes Stephen Jay Gould (1992):

"I can only conclude that someone once wrote the material this way
for a reason lost in the mists of time, and that authors of textbooks
have been dutifully copying ... ever since. ... evidence indicates
that cloning bears a .... discouraging message. It is the easy way
out, a substitute for thinking and striving to improve."

FOUR MORE COMMENTS:

I. As to whether or not one can regard the Sun's rays as emanating
radially from the Sun, Hugh Haskell (2003) had some comments (I'm not
sure I completely understand them):

HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH
I've been thinking about [Brian Whatcott's 18 Sep 2003 22:29:51-0500 Phys-L
comment}:

"I wonder what the evidence is for a preponderance of solar emission
in the radial direction? I don't see that much darkening of the disk
at the margin...."

I think he [Whatcott] has a point. If the "rays" really do amount to
photons, they are emitted without directional preference by the atoms
in the solar photosphere. Some will follow "radial" paths with
respect to the center of the sun, but most won't. But the net effect
is that about the same number of photons leave the sun in any
direction, so that when we are a great distance from the sun, all the
photons we receive are coming in essentially the same direction, and
that is *radial* relative to the center of the sun.

The reason that the sun seems so well-defined is because the
photosphere is very thin compared to the radius of the sun, so there
is very little angular distance as seen from the earth where the
visible light from the sun goes from a maximum to essentially zero.
But since those photons that get to the earth from the limb have
passed through more of the solar atmosphere than those coming from
the center of the sun's face, there is some limb darkening, just not
very much. If the photosphere were thicker, there would be more limb
darkening, and the edge of the solar disc would seem fuzzy.

But I think his point was well-taken [possibly referring to the
misattributed Woolf]. The reason that we can think of the light rays
from the sun as being "radial" is that at our distance from the sun,
all the photons that reach the earth left the sun heading is very
nearly the same direction, and that is parallel to the line joining
the centers of the sun and the earth--*radial.* If our distance from
the photosphere was small compared to the solar radius, we would see
light arriving from directions covering a significant fraction of the
hemisphere facing the sun, and would no longer talk about the rays
being radial.
HHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHHH

II. With regard to my list [Hake 2003a)] of critical aspects of
Seasons, Igal Galili (2003) wrote:

In a real instruction you do not need to name all possible
preconditions (we will never end the list...). Thus, you might focus
on (a) Earth's circular orbit (b) the tilt of its axis (c) light flux
striking a particular area. The rest can be left for the hermeneutic
learning of an individual. . . ."

In my opinion, my listing of

"f. The Earth's angular velocity vector omega, due to daily rotation
about its own axis, remains almost CONSTANT IN DIRECTION during the
Earth's orbit around the Sun (conservation of angular momentum)"

cannot be "left for the hermeneutic learning of an individual" [For a
discussion of "hermeneutics" see Phillips (2000)].

In Hake (2003b), I attempt to GUIDE students to understand "f"
(above) by having them walk slowly around a 20-ft-diameter circle
(simulating the Earth's path around the Sun) holding the handles of a
spinning bicycle wheel, while exerting only forces on the handles
such as to (a) keep the wheel from falling to the floor, and (b)
cause the relatively small centripital acceleration of the wheel in
its path around the 20-ft-diameter circle.


III. Dewey Dykstra (2003) quotes Hake (2003a): ". . . my own belief
is that middle-school students could be guided to construct a
reasonably good understanding of the seasons (and even phases of the
moon) by means of Socratic Dialogue Inducing (SDI) Labs. . ."

and then comments:

"Of course it depends on what "guided" means, but a strong case can
be made that "guiding" would not even be necessary, merely a pedagogy
that engages students in making sense of the available
experiences/data."

I wonder if Dewey thinks that students would be able to construct a
professional physicist's understanding of "conservation of angular
momentum" if given a "a zero-guidance "pedagogy that engages students
in making sense of the available experiences/data"?


IV. Regarding textbook diagrams, Bernard Cleyet wrote (slightly edited):

"It does appear that Chapter 2 of "Eyes on the Sky. . ." [SAO (1998)]
is for teachers. Therefore, the 'job' is to ensure teachers have the
background to know that the figures, inter alia, are only schematic."

More generally, the crucial question, not effectively addressed by
the NRC [Labov (2003)], AAAS "Project 2061," NSTA's "Scope, Sequence,
and Coordination," Lederman's "Physics First," and those seeking to
get science (such as the Seasons) across to middle-school students,
was asked by the insightful Arnold Arons [see Hake (2002a) for a
discussion]:

"WHENCE DO WE GET THE TEACHERS with the background, understanding,
and security to implement such instruction? They will certainly not
emerge from the present production mills. . ." (My CAPS.)

This brings us back to #10 of the NRC-ignored [McCray et al. (2003),
Labov (2003)] Lessons of the Physics Education Reform Effort [Hake
(2002b)]:

LESSON #10. A MAJOR PROBLEM FOR UNDERGRADUATE EDUCATION IN THE UNITED
STATES IS THE INADEQUATE PREPARATION OF INCOMING STUDENTS, IN PART
DUE TO THE INADEQUATE UNIVERSITY EDUCATION OF K-12 TEACHERS.

Richard Hake, Emeritus Professor of Physics, Indiana University
24245 Hatteras Street, Woodland Hills, CA 91367
<rrhake@earthlink.net>
<http://www.physics.indiana.edu/~hake>
<http://www.physics.indiana.edu/~sdi>

REFERENCES ARE IN PART 2