Explanation: What are those colorful rings around the Sun? A corona visible only to Earth observers in the right place at the right time. Rings like this will sometimes appear when the Sun or Moon is seen through thin clouds. The effect is created by the quantum mechanical diffraction of light around individual, similarly-sized water droplets in an intervening but mostly-transparent cloud. Since light of different colors has different wavelengths, each color diffracts differently. Solar Coronae are one of the few quantum color effects that can be easily seen with the unaided eye. This type of solar corona is a visual effect due to water in Earth's atmosphere and is altogether different from the solar corona that exists continually around the Sun -- and stands out during a total solar eclipse. In the foreground is the famous Himalayan mountain peak Ama Dablam (Mother's Necklace),
Re: APOD: A Colorful Solar Corona over the... (2016 Jan 11)
Posted: Mon Jan 11, 2016 5:23 am
by yasgur
Hah! It's either the above or you've got cataracts. Just had my eyes done.
Re: APOD: A Colorful Solar Corona over the... (2016 Jan 11)
Posted: Mon Jan 11, 2016 5:52 am
by Beyond
What an unusually nice picture of our neighborhood star. My first thought when i saw it, was 'Ann'. I think It would make a very good avatar for a color commentator.
Re: APOD: A Colorful Solar Corona over the... (2016 Jan 11)
Posted: Mon Jan 11, 2016 6:03 am
by Guest
When it says "A corona visible only to Earth observers", is that just badly worded? I would have thought that a corona would be visible of any planet (Venus & gas giants excluded), including Pluto and moons with atmospheric vapor, where diffraction may occur. Would it matter what the atmospheric vapor was made of? Would a cloud of (perhaps) methane diffract differently?
Re: APOD: A Colorful Solar Corona over the... (2016 Jan 11)
Posted: Mon Jan 11, 2016 6:41 am
by Chris Peterson
Guest wrote:When it says "A corona visible only to Earth observers", is that just badly worded? I would have thought that a corona would be visible of any planet (Venus & gas giants excluded), including Pluto and moons with atmospheric vapor, where diffraction may occur. Would it matter what the atmospheric vapor was made of? Would a cloud of (perhaps) methane diffract differently?
I think it just means it's an atmospheric phenomenon, nothing to do with the Sun itself. Not that similar coronas wouldn't be visible from some other bodies.
Re: APOD: A Colorful Solar Corona over the... (2016 Jan 11)
Posted: Mon Jan 11, 2016 7:23 am
by Ann
Beyond wrote:What an unusually nice picture of our neighborhood star. My first thought when i saw it, was 'Ann'. I think It would make a very good avatar for a color commentator.
Thanks, Beyond! It's flattering to be associated with a fine photograph. This APOD is indeed very nice and colorful.
I'll stick to my Pleiades avatar, though.
Ann
Re: APOD: A Colorful Solar Corona over the... (2016 Jan 11)
Posted: Mon Jan 11, 2016 9:12 am
by manfred the cat
Hi everyone,
I'm just wondering why it is said that the effect is "quantum mechanical diffraction of light"? Just because photons are both particles and waves? One usually do not describe a regular rainbow as being "quantum". Diffraction is not a quantum phenomenon, light dispersion isn't either. Am I missing something?
Thanks for your comments.
jl.
Re: APOD: A Colorful Solar Corona over the... (2016 Jan 11)
Posted: Mon Jan 11, 2016 9:32 am
by geckzilla
manfred the cat wrote:Hi everyone,
I'm just wondering why it is said that the effect is "quantum mechanical diffraction of light"? Just because photons are both particles and waves? One usually do not describe a regular rainbow as being "quantum". Diffraction is not a quantum phenomenon, light dispersion isn't either. Am I missing something?
Thanks for your comments.
jl.
This is presumably something very like the double-slit experiment except that these round droplets are doing the diffraction and somehow creating a giant corona.
Re: APOD: A Colorful Solar Corona over the... (2016 Jan 11)
Posted: Mon Jan 11, 2016 9:45 am
by manfred the cat
er... I'm not sure of the similarity, but OK, that's a lead...
Re: APOD: A Colorful Solar Corona over the... (2016 Jan 11)
Re: APOD: A Colorful Solar Corona over the... (2016 Jan 11)
Posted: Mon Jan 11, 2016 11:14 am
by Lasse H
The first thing that struck me was the slight asymmetry of the circles (wider at the top and narrower at the bottom). Nobody else seems to have commented on this. Is the explanation complex, or is it just to do with the camera (some kind of non-orthographic projection due to the optics)?
Re: APOD: A Colorful Solar Corona over the... (2016 Jan 11)
Posted: Mon Jan 11, 2016 11:41 am
by Les Cowley
The first thing that struck me was the slight asymmetry of the circles (wider at the top and narrower at the bottom).
Coronae can be distorted in shape if there are variations in cloud droplet size. In the extreme the corona becomes disordered cloud iridescence http://www.atoptics.co.uk/droplets/irid1.htm
However, this one looks like lens distortion. The image is very strongly enhanced indeed and coronae are never this colourful.
Re: APOD: A Colorful Solar Corona over the... (2016 Jan 11)
I agree. The wavelengths are 1000s of times larger than atomic sizes-- it's an entirely classical effect. Probably goes beyond geometrical optics, but that's all.
Re: APOD: A Colorful Solar Corona over the... (2016 Jan 11)
Posted: Mon Jan 11, 2016 2:53 pm
by Chris Peterson
manfred the cat wrote:Hi everyone,
I'm just wondering why it is said that the effect is "quantum mechanical diffraction of light"? Just because photons are both particles and waves? One usually do not describe a regular rainbow as being "quantum". Diffraction is not a quantum phenomenon, light dispersion isn't either.
Diffraction requires quantum mechanics for a complete description. It is reasonably called "quantum mechanical". However, since this particular phenomenon is adequately described by the classical treatment of diffraction (and far simpler than a QM analysis!), the qualification in this case seems unnecessary and potentially confusing.
Re: APOD: A Colorful Solar Corona over the... (2016 Jan 11)
Re: APOD: A Colorful Solar Corona over the... (2016 Jan 11)
Posted: Mon Jan 11, 2016 7:32 pm
by neufer
Douglas Hofstadter wrote:
<<"In the end, we self-perceiving, self-inventing, locked-in mirages are little miracles of self-reference. […] Our very nature is such as to prevent us from fully understanding its very nature. Poised midway between the unvisualizable cosmic vastness of curved spacetime and the dubious, shadowy flickerings of charged quanta, we human beings, more like rainbows and mirages than like raindrops or boulders, are unpredictable self-writing poems — vague, metaphorical, ambiguous, and sometimes exceedingly beautiful."
- (Epilogue: _I Am a Strange Loop_, p. 363 )
Re: APOD: A Colorful Solar Corona over the... (2016 Jan 11)
Posted: Mon Jan 11, 2016 8:09 pm
by heehaw
We are all quantum-mechanical now.
Re: APOD: A Colorful Solar Corona over the... (2016 Jan 11)
Posted: Mon Jan 11, 2016 8:14 pm
by Boomer12k
Spectacular....I saw a different phenomena...at least for me....the Sun was behind and above some clouds, nestled away....It was a lot like the video where the Sun sets at the Golden Gate Bridge awhile back...a lower image of the Sun kind of elongated the look of it.... like a ball with a lower knob. Did not get a pic of it as by the time I would have gotten back out, it might have been gone.
:---[===] *
Re: APOD: A Colorful Solar Corona over the... (2016 Jan 11)
Posted: Mon Jan 11, 2016 9:50 pm
by geckzilla
Chris Peterson wrote:
manfred the cat wrote:Hi everyone,
I'm just wondering why it is said that the effect is "quantum mechanical diffraction of light"? Just because photons are both particles and waves? One usually do not describe a regular rainbow as being "quantum". Diffraction is not a quantum phenomenon, light dispersion isn't either.
Diffraction requires quantum mechanics for a complete description. It is reasonably called "quantum mechanical". However, since this particular phenomenon is adequately described by the classical treatment of diffraction (and far simpler than a QM analysis!), the qualification in this case seems unnecessary and potentially confusing.
IIRC this isn't the first time quantum mechanics has been confusingly invoked in an APOD description. Checking... yes. The last time was here: http://asterisk.apod.com/viewtopic.php?t=34872
Re: APOD: A Colorful Solar Corona over the... (2016 Jan 11)
Posted: Mon Jan 11, 2016 10:04 pm
by heehaw
This is a good discussion, actually. Got me thinking. I really suggest an APOD of a white dwarf (Procyon and its wd companion would be ideal) and refer to Procyon and its quantum-mechanical white dwarf companion. That would be a use of "quantum-mechanical" that would be totally appropriate, because the only thing that keeps a white dwarf star from collapsing is the Heisenberg Uncertainty Principle, which is unequivocally quantum mechanical. And yet the object, the star, is macroscopic!
Re: APOD: A Colorful Solar Corona over the... (2016 Jan 11)
Posted: Mon Jan 11, 2016 10:16 pm
by heehaw
White dwarf as quantum-mechanical object? yes! the uncertainty principle is Δr × Δp = h (Planck constant). Each electron in Sirius B is confined to such a tiny Δr that Δp (the uncertainty in the momentum) must be very great, no matter how cold the gas is! So, it can't collapse! (at still higher pressures, the electrons merge with the protons and form neutrons, and so collapse does occur, until the quantum-mechanical momentum of the neutrons provides support, and now you have a neutron star.) Really extremely simple physics, with huge intellectual consequences!
Re: APOD: A Colorful Solar Corona over the... (2016 Jan 11)
Posted: Mon May 04, 2020 12:35 am
by neufer
Click to play embedded YouTube video.
heehaw wrote: ↑Mon Jan 11, 2016 10:04 pm
This is a good discussion, actually. Got me thinking. I really suggest an APOD of a white dwarf (Procyon and its wd companion would be ideal) and refer to Procyon and its quantum-mechanical white dwarf companion. That would be a use of "quantum-mechanical" that would be totally appropriate, because the only thing that keeps a white dwarf star from collapsing is the Heisenberg Uncertainty Principle, which is unequivocally quantum mechanical. And yet the object, the star, is macroscopic!
A Colorful Solar Corona over the Himalayas
