Re: sun n earth


Barry Schwarz wrote:
On Sat, 2 Sep 2006 18:52:26 +0530, "tree" <nospam@invalid> wrote:

does only 1 half of d earth sees sun r do sun rays difract

Even without an atmosphere to bend the sun's rays (such as with the
moon), sunlight will strike slightly more than half the surface simply
because the sun has a greater radius that the object being struck.
Consider the following geometric model for an intuitive description:

Put the sun at the origin (0,0) with radius R.

Put the object being struck at (2R,0) with radius r << R (<< means
much less than and +x is to the right).

Draw the upper and lower exterior common tangents between the two
circles (ignore the two interior crossing common tangents).

The upper tangent has a negative slope and the lower one a positive
slope and the two meet somewhere off to the right (this is the
explanation for annular eclipses).

Draw the radius from each tangent point on the object to the center
(2R,0). These two radii form a pattern similar to <. There is more
sunlit area to the left of the radii than dark area to the right.

The only time exactly half of the object would be illuminated is when
the two radii form a | which implies r = R. If r > R, less than half
the object is illuminated.

Once you throw in diffraction, it tends to expand the visual radius of
the sun thereby increasing the amount of area illuminated. Consider
the real world phenomenon of observing the sun from the poles during
the equinox. Without bending, the sun should appear right on the
horizon. However, it is known to appear degrees above the horizon at
both poles simultaneously.


Remove del for email

I have to laugh at the ' real world phenomen' expressed in geocentric
terms.

The orbital orientation of the Earth changes against fixed axial
orientation,within the next 3 weeks,that orbital orientation will run
almosts parallel with terrestial longitudes sweeping through the
orbital shadow/radiation division. at dawn and dusk.

http://upload.wikimedia.org/wikipedia/commons/a/a3/Seasonearth.png

Downplaying axial orientation and highlighting the change is orbital
orientation iwill be a major task,at least for those who wish to
promote climate studies.You were doing quite well until you started to
lapse into geocentric thinking,the way to alter this view is to take
note of oscillating temperature bands as a means to grasp the sheer
size and power of our parent star,the changing orbital orientation in
accoradnce with Keplerian geometry among many other things.

http://www.climateprediction.net/images/sci_images/annual.gif

.

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