Why don't neutrinos interact much with matter?

[t00fri]

...
The reason I even remember his second name over the same time span is simply because I stole it for a character in a short story. (The nerdy protagonist's name, "Lester Nussenzveig", was unfortunately the part of the story that worked best.) The initials I only encountered when I did a quick web search on "Nussenzveig" and "glory" to check the time-frame matched what you were talking about.

That's cute;-)

That's certainly compatible with what I'm reading ... I was getting a sense of disgruntlement from Greenler about the complexity of the maths required to predict the sizes of the coloured rings.

In fact, Nussenzveig's successful predictions of the subtle color phenomena in the glory were truly original. The color aspects were considered among the toughest challenges for everyone attempting a theoretical discussion of the glory!

Ah, typing up papers on a manual typewriter with carbon paper. How much fun was that?
I think I don't understand enough to get the full amusing historical effect, though it occurs to me I haven't heard the phrase "bag confinement model" for a long time ...

Grant

Usually my wife has filled in the math formulae by hand, since her handwriting is /infinitely/ better and significantly faster than mine. I am one of those lefthanders who were still forced to write with their right i.e. wrong hand. The result can easily be imagined...

We would typically write the manuscripts with pencil by hand and then dump it in the CERN typing pool for typing...Making corrections was a pain, though. The published version, used to look quite OK.

Bye Fridger

[t00fri]

...
There's another lighting effect that crops up around the antisolar point, which you often see around an aeroplane shadow when flying low over grass or cropland. On foot, you can see it at sunrise when there's dew on the grass:

It's very evident once you have it pointed out to you, but remarkably few people seem to notice it spontaneously.
It's called heiligenschein, and I wrote a bit about it for a Scottish newspaper a few years ago: it comes in two varieties, wet heiligenschein (the brighter kind you usually see in dew-covered grass) and dry heiligenschein (which is the kind you usually see from aircraft). Dry heiligenschein also seems to be a feature of lunar dust, at least on the maria explored by Apollo ... several astronauts reported that the shadow of their helmets on the dust was always surrounded by a bright nimbus.
I spoke to a bush pilot after the Zambian total solar eclipse a few years ago, and he said that he was in flight during the onset of the partial phase. He could see the patch of heiligenschein around his plane gradually turning crescent-shaped below him!

Grant

Thats interesting. I must confess that I never thought much about the physics of the Heiligenschein. Superficially, it does seem to be quite different from the Glory? Right?

Bye Fridger

[t00fri]

I was going to say "that's what you see around a shadow of a plane", because I've noticed that on a couple of occasions (never realised exactly what it was, but I figured it was an optical effect of some sort), but then you showed the photo that was clearly taken by a person on the ground. I didn't know it had a specific name though

Evil Dr.,

perhaps its worth adding that the dark shadow of some human being seen in the above photos is mainly serving to define the 180 degree angle wrto the sun. The sun is hidden behind that unknown person's head. The person is looking 180 degrees away from the sun while taking the photograph of his/her own "Glory";-)

Bye Fridger

[granthutchison]

Thats interesting. I must confess that I never thought much about the physics of the Heiligenschein. Superficially, it does seem to be quite different from the Glory? Right?

Pure reflection. Dry heiligenschein is really just an effect of the geometry of light and shade. Wet heiligenschein is brighter because a spherical water droplet brings light to a crude focus about 0.7R behind the drop. Since dew often sits on tiny hairs protruding from grass blades, this creates a brightly illuminated spot on the grass leaf itself ... scattered light from this retraces the journey through the dewdrop and comes out roughly collimated into a beam a few degrees across, retracing the angle of the incident light.

Grant

[startaq]

Is this the same phenomenon?



http://antwrp.gsfc.nasa.gov/apod/ap040913.html

[granthutchison]

Is this the same phenomenon?

No. The coloured ring means it's not heiligenschein, and the strict spectral arrangement of the colours means it's not a glory. That's why APOD posed it a mystery photograph, and I'm looking forward to their promised revelation of what's really going on in that one.

Grant

PS: My own theory (probably wildly wrong) is that it involves a liquid or solid with a higher refractive index than water ... so we're seeing a miniature rainbow, subtending far less than the angular diameter of a water rainbow.

[eburacum45]

Glass beads, I think, out of reflective paint or something similar.

[granthutchison]

Glass beads, I think, out of reflective paint or something similar.

They need to be pretty small ... there's a degree of diffractive spreading which is turning the central part of the rainbow pale, more like a fogbow.

Grant

[eburacum45]

Diffractive like in a diffraction grating? some kind of quantum thing? Non-classical? That is spooky...

[granthutchison]

Diffractive like in a diffraction grating? some kind of quantum thing? Non-classical? That is spooky...

You can see diffraction everywhere - it forms the glory we've been discussing, as well as the common coronal rings around the Sun and Moon. In the case of a rainbow, the tiny diameter of the water droplets induces diffraction which causes each wavelength of light to emerge at a range of angles rather than at the specific angle predicted by simple refraction and reflection. So you have a narrow band of green partially superimposed on a band of yellow, which is partially superimposed on orange, and so on. So the rainbow colours aren't fully saturated, but mixed together (the finite angular diameter of the Sun also contributes to this smearing). As the droplets get smaller, the diffraction effect gets greater, and the colours overlap more and more. Eventually, in a fogbow, they are so mixed together that you can see only the red and blue margins of the bow, with nothing but white visible between.
It might just be an effect of the colour reproduction of the image we're discussing, but I'm seeing the central green portion very undersaturated compared to the blue and red edges, making me think there's a significant degree of diffractive mixing going on.

Mind you, the apparent diameter of this whole rainbow is small, so diffraction and the angular diameter of the Sun are going to have a greater proportional effect on the colours than they would have in a conventional rainbow. Second thoughts therefore suggest that the beads or droplets creating the effect don't really need to be very small at all ... :oops:

Grant

[t00fri]

Diffractive like in a diffraction grating? some kind of quantum thing? Non-classical? That is spooky...

Not spooky, just another well understood facet of physics: depending on the product of R, the size of the object that scatters light and the wave number k=2Pi/wavelength, light behaves very differently.

-- in on extreme, it behaves like a point particle of classical mechanics, propagating along straight lines, the so-called light rays. This is the familiar limit of "geometrical optics" which most people have learned about a little at least in school...

--the other case concerns the regime where the wave nature of light becomes conspicuous. This is also the regime, where diffraction effects arise.

Light can penetrate into the geometrical shadow i.e. classically forbidden regions due to its wave nature!

Analogous phenomena should be familiar from the various wave length bands in radio receivers. The FM radio band, comprising "ultra short" radio waves (wavelength < 1meter) has trouble with obstacles > 1meter. A house in the way may be enough for bad reception. Propagation takes place essentially along straight line trajectories. The "long wave" band is much better here. The long radio waves can easily surmount hills and other obstacles like a "snake", since the wave length has similar dimensions as the size of these obstacles!

Bye Fridger

[granthutchison]

Glass beads, I think, out of reflective paint or something similar.

Yes. If it's an uncropped picture from a standard 35mm lens, then the rainbow radius is ~12-15 degrees, which corresponds to a refractive index of 1.6-1.65, which would be on the money for glass. I can't imagine mineral oil forming beads on a surface, so it's more likely solid than liquid. The very bright reflection in the middle implies really good internal reflection, though, so I'd guess they were silvered on the back surface.

So: a constructed reflective surface composed of glass beads in a reflective matrix, like one of those road-signs that "lights up" in your headlights.

Grant

[Matt McIrvin]

So: a constructed reflective surface composed of glass beads in a reflective matrix, like one of those road-signs that "lights up" in your headlights.

Walking around in the city, I've often seen those rainbows caused by reflective road paint. They're easy to see when the stripes on the road have just been repainted: the little beads end up scattered more widely than just the stenciled white region, and you can see rainbows in the asphalt.