APOD: Moon Corona, Halo, and Arcs over... (2020 Feb 24)

[APOD Robot]

Moon Corona, Halo, and Arcs over Manitoba

Explanation: Yes, but could you get to work on time if the Moon looked like this? As the photographer was preparing to drive to work, refraction, reflection, and even diffraction of moonlight from millions of falling ice crystals turned the familiar icon of our Moon into a menagerie of other-worldly halos and arcs. The featured scene was captured with three combined exposures two weeks ago on a cold winter morning in Manitoba, Canada. The colorful rings are a corona caused by quantum diffraction by small drops of water or ice near the direction of the Moon. Outside of that, a 22-degree halo was created by moonlight refracting through six-sided cylindrical ice crystals. To the sides are moon dogs, caused by light refracting through thin, flat, six-sided ice platelets as they flittered toward the ground. Visible at the top and bottom of the 22-degree halo are upper and lower tangent arcs, created by moonlight refracting through nearly horizontal hexagonal ice cylinders. A few minutes later, from a field just off the road to work, the halo and arcs had disappeared, the sky had returned to normal -- with the exception of a single faint moon dog.

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[neufer]

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[starsurfer]

The Age of Aquarius is coming!

[neufer]

The Age of Aquarius is coming!

The First Point of Aries defines the ecliptic coordinate of (0°, 0°). It is on the celestial equator at both the left and right extremes of the sky chart, with the ecliptic (the orange dotted sine curve) passing through it.

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<<Astrologers do not agree on when the Aquarian age (i.e., the First Point of Aries lying in the constellations of Aquarius) will start or even if it has already started. In 1929 the International Astronomical Union defined the edges of the 88 official constellations. The edge established between Pisces and Aquarius officially locates the beginning of the Aquarian Age around CE 2600. Many astrologers dispute this approach because of the varying sizes and overlap between the zodiacal constellations. They prefer to have the 12 zodiacal constellations be of uniform size (30 degrees along the ecliptic). Based on Nicholas Campion's research, most published materials on the subject state that the Age of Aquarius arrived in the 20th century (29 claims), with the 24th century in second place with twelve claimants.>>

[ta152h0]

Science is blowing up all my transistors in my head, releasing factory smoke. Have to go to Radio Shack & get replacement transistors. In the meantime, keep up the great work! Pass the ice cold one again, please!

[orin stepanek]

There's that Corona word again! I wonder if a cold
Corona Beer would help! Any way todays APOD is very nice!

Especially with the Moonbow like colors radiating around Luna!

[Ann]

There's that Corona word again! I wonder if a cold
Corona Beer would help! Any way todays APOD is very nice!


MoonHalo_Mckean_960.jpg


Especially with the Moonbow like colors radiating around Luna!

Hey, Orin, you said it all!

Except...look at that Big Eye in the sky....👁‍🗨

Ann

[orin stepanek]

There's that Corona word again! I wonder if a cold
Corona Beer would help! Any way todays APOD is very nice!


MoonHalo_Mckean_960.jpg


Especially with the Moonbow like colors radiating around Luna!

Hey, Orin, you said it all!

Except...look at that Big Eye in the sky....👁‍🗨

Ann

Would you say blue eye; or pink eye! Never saw a multicolored eye before! (ha ha)

[drjhammond]

Maybe someone can explain the term "quantum corona" in the text accompanying this APOD. The corona observed in this image (as is any such corona around the sun or moon) is produced by diffraction of light from small ice particles (sometimes water droplets but I assume not in this case) and is a classical optical phenomenon not a quantum effect. This phenomenon is seen frequently but it is always beautiful to see and if the thin clouds or atmosphere contain ice crystals the 22 degree halo is often visible. The tangent arcs and parhelia (sun dogs--parselenia ? and moon dogs?) are rarer. The message is: keep looking up! It is interesting to note that when sun dogs or moon dogs are seen when the sun or moon is near the horizon they lie closer to the 22 degree halo than when they occur higher in the sky. The best place to read about these phenomena is here: atoptics.co.uk/

[neufer]

Maybe someone can explain the term "quantum corona" in the text accompanying this APOD. The corona observed in this image (as is any such corona around the sun or moon) is produced by diffraction of light from small ice particles (sometimes water droplets but I assume not in this case) and is a classical optical phenomenon not a quantum effect.

It is indeed a classical optical phenomenon if you think of light as a (λ>0) wave.

However, it is a "quantum" optical phenomenon if you think of light as particles (i.e., photons).

The standard practice nowadays is to treat:

• 1) simple rainbows using (λ=>0) light ray caustics as classical and
  2) more complicated (λ>0) diffraction phenomenon as "quantum."

[drjhammond]

Sorry to repeat myself, but diffraction is a result of the wave nature of light, not the particle nature. I don't know why "standard practice" would now say that erroneous statements would be true. You get the interference that produces colors from the wave nature of light and you get the spreading of the light also because of the wave nature of light. Similarly, the wave nature of particles such as electrons, can be observed with diffraction with single or double (or multiple) slits. The colors you see when light is reflected from a diffraction grating such as the surface of a CD or DVD is the result of interference of different wavelengths which diffract at different angles from such a grating. The small ice crystals which have a relatively uniform spacing in thin clouds also can produce reinforced color at particular angles in a similar manner. Maybe some other reference to such "standard practice" would help me understand why the term is used in this way.

[neufer]

Sorry to repeat myself, but diffraction is a result of the wave nature of light, not the particle nature. I don't know why "standard practice" would now say that erroneous statements would be true. You get the interference that produces colors from the wave nature of light and you get the spreading of the light also because of the wave nature of light. Similarly, the wave nature of particles such as electrons, can be observed with diffraction with single or double (or multiple) slits. The colors you see when light is reflected from a diffraction grating such as the surface of a CD or DVD is the result of interference of different wavelengths which diffract at different angles from such a grating. The small ice crystals which have a relatively uniform spacing in thin clouds also can produce reinforced color at particular angles in a similar manner. Maybe some other reference to such "standard practice" would help me understand why the term is used in this way.

Almost all practical optics (e.g., design of lens, reflecting telescopes, etc.) are based upon:

• 1) geometric light rays
  2) their caustics
  3) and the (color dependent) refraction of index for different materials.

Ray optics is also sufficient for a basic understanding of most atmospheric effects (e.g., rainbows, glories, etc.).

Assigning diffraction & interference effects with the designation "quantum" is simply
a cutesy way of pointing out that such effects can be ignored in most cases.
(Have a cup of Maxwell House & chill.)

[drjhammond]

I haven't figured out how to insert a quote from the previous comment.

I'm not trying to quibble with how people want to think about optical effects but it's important to use terminology correctly. Therefore, in comments about and within a discussion about real science, I think terminology is important. Ray optics doesn't work well to explain interference or diffraction and glories, coronas and some other atmospheric optical phenomena can be described with wave optics but quantum effects are not necessary for such descriptions.

[neufer]

I haven't figured out how to insert a quote from the previous comment.

Every previous comment has a curly quotation mark button in the upper right to hit: “
(For the first 24 hr there are also edit & delete buttons available up there.)

I'm not trying to quibble with how people want to think about optical effects but it's important to use terminology correctly. Therefore, in comments about and within a discussion about real science, I think terminology is important. Ray optics doesn't work well to explain interference or diffraction and glories, coronas and some other atmospheric optical phenomena can be described with wave optics but quantum effects are not necessary for such descriptions.

Almost all atmospheric optical phenomena are described using Ray Optics.

The APOD writers seem to like to think of these light rays as photon trajectories
under which circumstances it sort of makes sense to refer to the
secondary interference & diffraction phenomena as quantum effects.

If this forces you to consider what is actually going on in new
(all be it uncomfortable) ways then that is probably a good thing.

[drjhammond]

Almost all atmospheric optical phenomena are described using Ray Optics.

The APOD writers seem to like to think of these light rays as photon trajectories
under which circumstances it sort of makes sense to refer to the
secondary interference & diffraction phenomena as quantum effects.

If this forces you to consider what is actually going on in new
(all be it uncomfortable) ways then that is probably a good thing.

I guess we will have to agree to disagree about this. The most notable quantum effects observed in atmospheric optical phenomena are those seen as auroras and airglow in which quantized absorption and emission of radiation are responsible for the observed colors. I am not being forced "to consider what is going on in new ways" because these so-called "new ways" (calling interference a quantum phenomenon, for instance) are not correct ways to consider what is going on.

JAH out until I feel the need to respond to another correspondent.