W8KTZ St. Joe's High School Radio Club

---Member Activities---

--Discussions about the Solar Eclipse August 21, 2017--

Aaron Milavec W8TMY and Mike Stimac W8KTZ discuss their activities and thoughts,
and input from other members is always welcome!

From: Michael Stimac W8KTZ
To: Aaron Milavec W8TMY
Aug 23, 2017 at 10:23 AM

One more project done. We drove down to Kentucky, to Cadiz, which was 50 miles off dead center line, and therefor two seconds shorter in eclipse duration out of the 2-1/2 minutes. 10,000 people were expected in the dead-center town.

The show was dramatic. The air cooled suddenly, breeze slowed, and by the motel, the parking area lights came on!

Dramatic as it was, I have to admit to being spoiled by two Totals that I experienced in deserts -- 1972 in Kenya NFD desert, and 1991 in Mexico's Baja del Sur peninsula. There I saw the shadow bands on the sand, of what looked like a moving, rippling display of Fraunhofer bands: the corona looked smaller and this time birds and insects were absent.   Made me think of Rachel Carson's book, "Silent Spring".

The predicted mass migration of humanity occurred. It took us about 7 hours to reach Cadiz. The next afternoon,  a million, or multiple thereof of visitors, hit the road after the eclipse. The freeways locked up, and cars backed up for 2 miles from the entry ramps. We left at 3 in the afternoon, and got home at 5:30 in the morning!  --seventeen hours plus!!!!

The problem is our freeway access design. It took me a while to see the choke point but I think I have spotted it. At the top of the access ramp the entering cars do not have a long enough run to match the freeway speeding traffic. Thus they stop and wait for a break, whereupon a couple break into the traffic, and the line moves up, the empty interval in the traffic lineup, like a live bug, travels back thru the 2-mile string of inching cars! The speed-up parallel lane of the feeding ramp needs to be at least a 1/4 mile long (to accomodate eclipses a couple times each century !!!!)

But after all is said, to experience  the million-year old phenomenon, knowing what is really happening, makes one wonder what it was like when the light of the sun dimmed and one's world started getting dark and cold. Sure wasn't hard for the shamans to make a profit on the event! Once again, I feel that I paid proper dues to nature which has infinite illustrations of its secrets. mike

From: Aaron Milavec
To: Michael Stimac

Dear Mike,

I loved your reflections on the eclipse, including the mass migration of human observers in KY.

I believe that the Fraunhofer lines are the dark lines in the solar light spectrum caused by atmospheric absorption.  The bands of light on the sand are most probably produced by a diffraction phenomenon.  With the moon eclipsing the sun, the corona on opposite sides of the eclipse approximate two slits separated in space by the width of the moon.  The following article affirms this line of explanation: 1913ApJ....38..192B Page 192 http://adsabs.harvard.edu/full/1913ApJ....38..192B

When I just noticed the 1913 date of this article, however, I had my doubts.  So I searched further.  NASA (2017) supports the position that the bands of light are a refraction phenomenon like that of the moving light bands at the bottom of a swimming pool: The simplest explanation is that they arise from atmospheric turbulence. When light rays pass through eddies in the atmosphere, they are refracted. Unresolved distant sources simply "twinkle," [as when one observes stars in the night sky near the horizon] but for nearby large objects, the incoming light can be split into interfering bundles that recombine on the ground to give mottled patterns of light and dark bands, or portions of bands. Near totality, the image of the Sun is only a thin crescent a few arc seconds wide, which is about the same size as the atmospheric eddies as seen from the ground. 

[What are "shadow bands?" | Total Solar Eclipse 2017] --- https://eclipse2017.nasa.gov/what-are-shadow-bands

On Space.com, however, this phenomena is called a continued "mystery" and both the above explanations are given.  Special attention is given to the fact that most solar observers never observe the "shadow bands" because their ATTENTION is always directed up.  Not so in 1925 and 1978.

In the 20th century, two "vintage" years stand out so far as shadow-band visibility is concerned. The first case is the eclipse of Jan. 24, 1925. Since this event came a few days after a heavy snowfall for the Northeast United States, shadow bands were readily seen upon the fresh snow by most eclipse watchers. Meteorologist Edward Brooks who observed this eclipse from Groton, Connecticut, noted in 1978: "The snow offered offered the best backdrop for viewing the eerie fleeting shadow bands at any of the nine total eclipses I have gone to."

I also learn that the "shadow bands" are most clear just before and just after the total eclipse.  So my hat off to you, Mike, for observing the shadow bands on the sand in 2017!

Great discoveries!


Post Script #1: What does the observation that the shadow bands are most clear just before and just after the total eclipse (but not during the few minutes when the eclipse is total) say to me?

In my thinking, this observation tends to confirm the diffraction theory.  How so? 

During the total eclipse, opposite sides of the corona can be understood as small slits that produce diffraction interference bands.  During the total eclipse, these bands would form in every angular direction and this would tend to blur out the interference bands in any given angular direction. 

Before and the total eclipse, however, the sunlight on the leading side would be very bright and on the trailing side, dim.  Thus only faint diffraction lines would be produced along the axis of the sun's motion.  Perpendicular to this axis, however, the amount of light on both sides would be always equal --the best condition for the double slit interference.  If this explanation is correct, then the diffraction lines on the ground would always be perpendicular to the sun's movement (hence in the N-S rather than in the E-W direction).  No one to my knowledge has noted the direction of the the lines relative to the motion of the sun; hence, my hunch has yet to be tested.

The explanatory power of my hunch, however, is that it explains why the shadow bands are most clear just before and just after the total eclipse (but not during the few minutes when the eclipse is total).  The alternative explanation (atmospheric refraction) appears unable to account for this interesting observation.

Any ideas on this?  Anything I overlooked?

P.S.#2: Eurika! I just discovered research by Dr. Wolfgang Strickling that demonstrates that the shadow bands are always perpendicular to the (perceived) motion of the sun. [ www.strickling.net/ shadowbands.htm] http://www.strickling.net/shadowbands.htm

But Dr. Wolfgang Strickling uses his observation to fortify his theory that heat waves in the atmosphere cause the shadow bands.  He uses the single slit of the sun two minutes before and after the full eclipse by way of calculating the directionality of the shadow bands.  Hence he dismisses interference lines entirely.

Any further thoughts on Strickling?

P.S.#3: Dr. Eves says the lines are a due to a super-sonic boom created by the speed of the shadow of the moon projected on the face of the earth. 

Dr Eves says the speed of the Moon's shadow is generally supersonic and likens the phenomenon to the sonic boom of a jet breaking the sound barrier. But the sound pulses are not generated as single events. Instead, they are created continuously along a "shock front" which moves ahead of the eclipse itself.. ..

Dr Eves draws a comparison with the waves created when a ship travels through water. If this is correct, then it would explain why shadow bands seen before the eclipse would mostly travel in the direction of the eclipse shadow. After the eclipse, the shadow bands would travel at angles in the same way that waves diverge behind a ship.  [ Another question is whether this is observed? ] Thus Dr. Eves appears to have used his sonic boom model to explain the change in direction of the bands before and after the full eclipse.

Furthermore: Stuart Eves thinks that demonstrating a role for infrasound might explain some other puzzling phenomena associated with eclipses.

For example, long period Foucault pendulums - designed to demonstrate the rotation of the Earth - have been known to swing wildly during eclipses. Gasp!  This single observation [if it is true] shows that the mystery remains and that none of the theories (including my own) satisfactorily explains all the phenomena associated with solar eclipses.

Any thoughts on this?

P.S.#4: I checked into the issue of pendula and eclipses and, to my surprise, there does seem to be some truth here:

The Allais effect refers to the alleged anomalous behavior of a pendulum -- https://en.wikipedia.org/wiki/Pendulum,

--or gravimeter, -- https://en.wikipedia.org/wiki/Gravimeter

which is sometimes purportedly observed during a solar eclipse.


The effect was first reported as an anomalous precession

-- https://en.wikipedia.org/wiki/Precession of the plane of oscillation of a Foucault pendulum

-- https://en.wikipedia.org/wiki/Foucault_pendulum during the solar eclipse of June 30, 1954.

-- https://en.wikipedia.org/wiki/Solar_eclipse_of_June_30,_1954

-- above thoughts by Maurice Allais: -- https://en.wikipedia.org/wiki/Maurice_Allais, --as commented on by Aaron Milavec

The use of the words "alleged" and "purportedly" herein is my way of indicating that some scientists have "found a disturbance" while others "failed to notice anything." 

P.S.#5: Does one have here the observation of Michael Polanyi, "Every belief works in the eyes of the believer"?

So, the mysterious phenomena associated with solar eclipses continues to grow and so do the theories to explain these phenomena. . . .  

--- Aaron Milavec ---

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---updated June 20, 2019---

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