Comments and questions about the
APOD on the main view screen.
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orin stepanek
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by orin stepanek » Mon Sep 16, 2019 11:43 am
![Cool 8-)](./images/smilies/icon_cool.gif)
Beautiful Photo! Too bad it is vertical; so I can't use it as a background on my computer screen!
![Sad :(](./images/smilies/icon_sad.gif)
Orin
Smile today; tomorrow's another day!
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TheOtherBruce
- Science Officer
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by TheOtherBruce » Mon Sep 16, 2019 9:11 pm
Aren't they usually rounder than this? The shapes of the corona and the cloud give the impression Someone just lifted the lid on the outer crystal sphere so They could have a look inside...
This universe shipped by weight, not by volume.
Some expansion of the contents may have occurred during shipment.
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Chris Peterson
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by Chris Peterson » Mon Sep 16, 2019 9:36 pm
TheOtherBruce wrote: ↑Mon Sep 16, 2019 9:11 pm
Aren't they usually rounder than this? The shapes of the corona and the cloud give the impression Someone just lifted the lid on the outer crystal sphere so They could have a look inside...
The size of the corona is a function of the size of the diffracting particles. If you have clouds with different sized droplets in different zones, you'll get a distorted circle. If the cloud has different sized droplets all mixed together, you'll get a white, or nearly white corona.
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zeitoon
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by zeitoon » Tue Sep 17, 2019 2:11 am
What quantum mechanical diffraction effect are they talking about? I've been looking at papers and they all use a classical diffraction picture when talking about the lunar corona
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neufer
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by neufer » Tue Sep 17, 2019 3:08 am
zeitoon wrote: ↑Tue Sep 17, 2019 2:11 am
What quantum mechanical diffraction effect are they talking about?
I've been looking at papers and they all use a classical diffraction picture when talking about the lunar corona
Classical optics usually refers to geometrical/ray optics (using Snell's Law)
which can handle simple halos & rainbows.
Classical diffraction/interference is required to handle lunar corona & sophisticated rainbows.
APOD is just being a little coy in calling it
quantum mechanical
for
a situation where photons are clearly not being individually counted.
https://en.wikipedia.org/wiki/Geometrical_optics wrote:
<<The simplifying assumptions of geometrical optics include that light rays:
- propagate in straight-line paths as they travel in a homogeneous medium
bend, and in particular circumstances may split in two, at the interface between two dissimilar media
follow curved paths in a medium in which the refractive index changes
may be absorbed or reflected.
Geometrical optics does not account for certain optical effects such as diffraction and interference.>>
Art Neuendorffer
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Chris Peterson
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by Chris Peterson » Tue Sep 17, 2019 3:19 am
zeitoon wrote: ↑Tue Sep 17, 2019 2:11 am
What quantum mechanical diffraction effect are they talking about? I've been looking at papers and they all use a classical diffraction picture when talking about the lunar corona
Quantum mechanics is just a more complete way of dealing with classical diffraction. In this case, you could use either and get the same result.
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Goodwin
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by Goodwin » Tue Sep 17, 2019 3:17 pm
Thank You Chris Peterson! For pointing out that it's a diffraction effect, called Rayleigh scattering, that gives different (& small) diffraction angles for different particle sizes as well as for different wavelengths, and not refraction through water droplets or ice crystals as in rainbows, etc. that gives the same (& larger) angle for a given wavelength, independent of particle size. Rayleigh scattering also accounts for the sky being blue and sunsets red.
A more difficult question is why a guy who used to make a living doing diffraction of X-rays didn't immediately think of that....