APOD: Unusual Red Glow Over Minnesota (2009 Feb 17)

[neufer]

The camera is looking DOWN at more than 14°.

Maybe, but what matters if forward scatter is involved is the angle between the clouds and Sun, and that's quite small.

It's a total of more than 20° ...which is NOT small.

Besides, you've already stated that surface reflection is the dominant factor here
and there is negligible forward scattering surface reflection.

That said, the sun appears pretty darn small when reflected off of a sphere

But we're talking here about the reflections off of billions of spheres.
And of course, the illuminated area is still only a fraction as bright as the Sun itself.

Then why are these rainfall APODs so dark (except for the rainbows):
http://antwrp.gsfc.nasa.gov/apod/ap070912.html
http://antwrp.gsfc.nasa.gov/apod/ap060702.html

Where are those reflections off of billions & billions of spheres?
---------------------------------------------------------------------
Note: One should not confuse very dark rain fall
with either fine mist or thick jets of aerated water:

[Chris Peterson]

Maybe, but what matters if forward scatter is involved is the angle between the clouds and Sun, and that's quite small.

It's a total of more than 20° ...which is NOT small.

I'd say between about 5° on the left, and perhaps 20° on the right. Since I don't think it's scatter, that might not be important in that respect, but I think it might allow for additional insight into the phenomenon.

But we're talking here about the reflections off of billions of spheres.
And of course, the illuminated area is still only a fraction as bright as the Sun itself.

Then why are these rainfall APODs so dark (except for the rainbows):

I'm not sure they are dark at all. In fact, they are reflecting quite a lot of light, it's just not red, and the camera exposures are short. Nevertheless, there are many possible variations of droplet size, density, and illumination angle. Certainly, people here have reported seeing exactly this effect, and some excellent images were posted in this discussion that are virtually identical to what the airplane window shot shows. But while seeing rain illuminated by the orange sunset isn't rare, it certainly isn't a real common thing, either. So I have to assume it all comes down to the right conditions... like so many atmospheric phenomena.

[Skywatcher2]

TheSky6 says the sun set at 7:08 PM Minneapolis local time on 09/23/02. That would be within a minute of the time of the picture, not fifteen minutes.

Some adjustment to the sunset time, I don't know how much, needs to be made for altitude.

Good point. I hadn't thought of that. Probably a good thing I don't try to make a living at anything involving science or math that's more complicated than addition and subtraction.

You did get me curious about how much affect altitude would have though. From what I can gather looking for an answer on the internet, it looks to me like it would be about a minute per mile of altitude. Seems too low to me. I'm sure somebody will prove that wrong.

[geckzilla]

As an artist I think I might notice how color affects things a little more than the average person... the color of water is highly dependent on its lighting conditions and the environment. If the sky were red the ambient light would cause any shadows on the clouds to be pinkish and the rain may be a dull brown. If the sun is at least moderately high in the sky and the sky is still dominantly blue, we get whitish light blue clouds with dull blue gray rain. And then of course during sunset we get every color of pink, purple, red, orange, and yellow appearing. I'm still surprised by the incredulity I've seen in this thread. Oh well, I never thought I would read an argument over the semantics of virga, either.

[neufer]

But we're talking here about the reflections off of billions of spheres.
And of course, the illuminated area is still only a fraction as bright as the Sun itself.

Then why are these rainfall APODs so dark (except for the rainbows):
http://antwrp.gsfc.nasa.gov/apod/ap070912.html
http://antwrp.gsfc.nasa.gov/apod/ap060702.html

I'm not sure they are dark at all. In fact, they are reflecting quite a lot of light, it's just not red, and the camera exposures are short. Nevertheless, there are many possible variations of droplet size, density, and illumination angle.

The falling raindrops are ALL VERY dark (except for the embedded rainbow).

Certainly, people here have reported seeing exactly this effect, and some excellent images were posted in this discussion that are virtually identical to what the airplane window shot shows. But while seeing rain illuminated by the orange sunset isn't rare, it certainly isn't a real common thing, either. So I have to assume it all comes down to the right conditions... like so many atmospheric phenomena.

People here have MISTAKENLY reported what they THINK they see.

Show me ONE IMAGE of "orange rain" that you can certify is actually FALLING RAIN.

[Chris Peterson]

The falling raindrops are ALL VERY dark (except for the embedded rainbow).

I disagree. I think the falling raindrops are quite well lit, they simply look dark because the foreground is so much brighter, and because they are uniformly lit. I think that if those raindrops were actually in the shadow of a cloud, but with a single sunbeam illuminating a small area, you'd see that lit area as apparently bright (but white in that case, since the Sun isn't setting).

People here have MISTAKENLY reported what they THINK they see.

Show me ONE IMAGE of "orange rain" that you can certify is actually FALLING RAIN.

Clearly that's not going to be possible. I trust my own interpretation of what I've seen with my eyes, and I believe that the links to orange rain posted by geckzilla on page 6 of this discussion show exactly the same thing as the airplane window image, and I don't see any reason to think they aren't showing what they claim: rain lit by a setting Sun. In addition, the NOAA and Wikipedia pages on virga both mention that one of its features is the ability to catch the setting Sun and produce brilliant orange displays. In the images of sunlit virga, and where I've seen the effect, the sun, virga, and observer have been nearly lined up, and that describes the situation with the airplane shot as well. So overall, I consider the question settled. If you have a different opinion, that's fine. Since the situation can't be recreated, nobody can ever know with 100% certainty what the image shows.

[neufer]

The falling raindrops are ALL VERY dark (except for the embedded rainbow).
http://antwrp.gsfc.nasa.gov/apod/ap070912.html
http://antwrp.gsfc.nasa.gov/apod/ap060702.html

I disagree. I think the falling raindrops are quite well lit, they simply look dark because the foreground is so much brighter, and because they are uniformly lit. I think that if those raindrops were actually in the shadow of a cloud, but with a single sunbeam illuminating a small area, you'd see that lit area as apparently bright (but white in that case, since the Sun isn't setting).

Judging from the rainbows, the falling raindrops ARE quite well lit, they simply look dark because they ARE dark.

People here have MISTAKENLY reported what they THINK they see.
Show me ONE IMAGE of "orange rain" that you can certify is actually FALLING RAIN.

Clearly that's not going to be possible.

Clearly.

I trust my own interpretation of what I've seen with my eyes, and I believe that the links to orange rain posted by geckzilla on page 6 of this discussion show exactly the same thing as the airplane window image, and I don't see any reason to think they aren't showing what they claim: rain lit by a setting Sun. In addition, the NOAA and Wikipedia pages on virga both mention that one of its features is the ability to catch the setting Sun and produce brilliant orange displays.

The virga in question probably catches the setting sun because it is composed of ice crystals which are high enough to do so.

In the images of sunlit virga, and where I've seen the effect, the sun, virga, and observer have been nearly lined up, and that describes the situation with the airplane shot as well. So overall, I consider the question settled. If you have a different opinion, that's fine. Since the situation can't be recreated, nobody can ever know with 100% certainty what the image shows.

I'm nearly 100% certain that no so called image of "bright orange rain" is ever an image of actual falling raindrops.
There is absolutely no physics to justify such an assumption.

I enjoy The Asterisk* because I learn so much from others (especially from Chris) and because the absolute best way to learn is to attempt to teach what one thinks one knows...especially when one gets it wrong (as I have many times). I don't trust my own (nor anyone else's interpretations) without careful consideration (and reconsideration) and that is what makes me a good scientist...I think.

[aristarchusinexile]

I still have to go with window reflection .. the 'L' being my clue .. has the cause been revealed to us yet or are we still speculating?

[geckzilla]

Rain? Touching the ground, right?
http://upload.wikimedia.org/wikipedia/c ... _beach.jpg

As far as rain being dark sheets here is my crude understanding of why sometimes a sheet of rain will appear dark and ominous while at other times it will be brightly lit up.


If there is a thin sheet of rain, the rain is white or whatever color of light is hitting it. Orange in my picture. As rain drops add up and the rain sheet gets thicker (and probably more likely to actually be hitting the ground, right?) the droplets cast shadows on themselves and eventually no light can really make it through and we're left with whatever ambient light happens to be bouncing around which is usually from the atmosphere or some dim light that managed to make it through the cloud cover. Anyway, whatever it's called, rain, virga, slush, ice crystals, snow, or a piece of a cloud falling down...

[neufer]

Rain? Touching the ground, right?
http://upload.wikimedia.org/wikipedia/c ... _beach.jpg

Rain falling towards the ground (or towards the sea, if you prefer).

As far as rain being dark sheets here is my crude understanding of why sometimes a sheet of rain will appear dark and ominous while at other times it will be brightly lit up.

Actually, raindrops are oblate spheroids like the earth.

Fine mist doesn't fall and, hence, is spherical:
http://upload.wikimedia.org/wikipedia/c ... _beach.jpg

[foreststranger]

My picture I took one night from the ground, is the same sunset glow through light rain falling. http://home.roadrunner.com/~mikeh07/images/wall_5.jpg
I was taking a picture of a sunset rainbow, and turned around to the NW to see this display.
Mike

[geckzilla]

Er, yeah, I didn't think rain drops were really shaped like that. It's an iconic representation. Just like how the emote doesn't really look like a human face but we recognize it as one anyway.

[apodman]

... the emote doesn't really look like a human face but we recognize it as one anyway.

Several examples to the contrary:

http://www.cartoonstock.com/directory/s/smiley_face.asp

[southerncharmer2]

Perhaps I missed it, but did anyone totally confute the idea of the methane gas cloud emitted by the horses from the racetrack and stables below? It was my first thought since they DID mention the racetrack in the original description and this possibility WAS mentioned by at least one other contributor (mary.osterman Feb.17, 2009). I scanned the posts rather quickly, yet did not see any conversation concerning this theory, nor did I see a rebuttal to this contributor.

It may be a silly idea, since I'm not a scientist, but, in the presence of the weather conditions, lighting conditions, and jet fuel emissions, a methane gas cloud is just as plausible to me!

[Chris Peterson]

It may be a silly idea, since I'm not a scientist, but, in the presence of the weather conditions, lighting conditions, and jet fuel emissions, a methane gas cloud is just as plausible to me!

Methane is colorless, and even if it were not, any methane from the ground would be incredibly diffuse by the time it reached several thousand feet. If you're suggesting it was burning, the color is wrong, and the likelihood of the concentration being flammable is even smaller than the likelihood of a cloud of methane somehow remaining intact after rising thousands of feet.

[southerncharmer2]

I suppose methane was plausible to me, since, in my readings regarding Saturn's moon, Titan, I remember something being mentioned about the methane in Titan's atmosphere being found near to water vapor, and the refraction of sunlight through the combination glowed orange.

To me, it made logical sense of something that no one has explained yet and just goes to prove you can't believe everything you read on the Internet!

Thank you for the clarifications!

[neufer]

I suppose methane was plausible to me, since, in my readings regarding Saturn's moon, Titan, I remember something being mentioned about the methane in Titan's atmosphere being found near to water vapor, and the refraction of sunlight through the combination glowed orange.

<<Tholin (after the Ancient Greek word θολός tholós for ”mud”), is a heteropolymer molecule formed by solar ultraviolet irradiation of simple organic compounds such as methane or ethane. The term "tholin" was coined by astronomer Carl Sagan to describe the difficult-to-characterize substances he obtained in his Urey-Miller-type experiments on the gas mixtures that are found in Titan's atmosphere. It is not a specific compound but is a term generally used to describe the reddish, organic component of planetary surfaces. Tholins do not form naturally on modern-day Earth, but are found in great abundance on the surface of icy bodies in the outer solar system. They usually have reddish-brown appearance.

"Triton tholin" and "Titan tholin" are nitrogen-rich organic substances produced by the irradiation of gaseous mixtures of nitrogen and methane such as that found in those moons' atmospheres; Triton's atmosphere is 99.9% nitrogen and 0.1% methane and Titan's atmosphere is 98.4% nitrogen and the remaining 1.6% composed of methane and trace amounts of other gases. These atmospherically derived substances are distinct from "ice tholin", which is formed by irradiation of clathrates of water and organic compounds such as methane or ethane. The plutino Ixion is also high in this compound.

The surfaces of comets, centaurs, and many icy moons in the outer solar system are rich in deposits of Triton, Titan and ice tholins. The haze and orange-red color of Titan's atmosphere and Centaur-class planetoids is thought to be caused by the presence of tholins. Tholins may also have been detected in the protoplanetary disk of young stars; see HR 4796A. Some researchers have speculated that Earth may have been seeded by organic compounds early in its development by tholin-rich comets, providing the raw material necessary for life to develop; see Urey-Miller experiment for discussion related to this issue. Tholins do not exist naturally on current-day Earth due to the oxidizing character of its atmosphere.

A theoretical model explains formation of tholins by the dissociation and ionization of molecular nitrogen and methane by energetic particles and solar radiation, formation of ethylene, ethane, acetylene, hydrogen cyanide, and other small simple molecules and small positive ions, further formation of benzene and other organic molecules, their polymerization and formation of aerosol of heavier molecules, which then coagulate and deposit on the planetary surface.

Tholins formed at low pressure tend to contain nitrogen atoms inside their molecules while tholins formed at high pressure display nitrogen atoms more likely located in terminal positions.

Tholins can act as an effective screen for ultraviolet radiation, protecting the planetary surface from it.

A wide variety of soil bacteria are able to use tholins as their sole source of carbon. It is thought tholins may have been the first microbial food for heterotrophic microorganisms before autotrophy evolved.>>

[geckzilla]

... the emote doesn't really look like a human face but we recognize it as one anyway.

Several examples to the contrary:

http://www.cartoonstock.com/directory/s/smiley_face.asp

Those aren't contrary to what I said. Bah, next time I make an illustration it's going to use smiley faces instead of whatever is supposed to be there.

[aristarchusinexile]

... the emote doesn't really look like a human face but we recognize it as one anyway.

Stick some ears on it and away we go.

[grbrowne]

Swamp gas from a weather balloon was trapped in a thermal pocket and reflected the light from Venus.

[apodman]

the emote doesn't really look like a human face

... http://www.cartoonstock.com/directory/s/smiley_face.asp ... aren't contrary to what I said.

Bear with me on this one. Imagine that I am an alien who has never seen a human face. I discover these cartoons as my only pictures of human faces. From my misinformed point of view, the emote resembles the human faces greatly - contrary to what you said. So I stretched a point and my humor is oblique. I was just employing a teaser to invite you (or anyone) to look at these pictures, which you did. I thought similar pictures I saw in the past were enjoyable, and I wanted to share my happiness. The humorous theme of most of the cartoons, in fact, is "what if" a smiley did really look like a human face (because, ha ha, a human face looked like a smiley) - an absurd take on your statement.

If you want to be totally serious, I agree that smileys are not realistic representations of living beings, and I believe that the point you made by saying so is totally valid - valid beyond question, so that anything said to the contrary could only be a joke. Either that or I'm too crazy to know the difference between a cartoon and a real human being, in which case you would be over your head trying to educate me.

[geckzilla]

That's funny, because to come to the conclusion that the smiley didn't look anything like a human, I actually did imagine that I was an alien. I think it's only recognizable if one understands the human concept of representation through simplified line drawings. For instance, a dog may recognize me instantly when he sees my face. If I showed him a large print of a pixel emote he probably would not even recognize it as having anything to do with any person. ...But then again I suppose there's no way to prove that. I don't know. My apologies if you were making a joke. I hate to come off as overly serious.

[aristarchusinexile]

That's funny, because to come to the conclusion that the smiley didn't look anything like a human, I actually did imagine that I was an alien. I think it's only recognizable if one understands the human concept of representation through simplified line drawings. For instance, a dog may recognize me instantly when he sees my face. If I showed him a large print of a pixel emote he probably would not even recognize it as having anything to do with any person. ...But then again I suppose there's no way to prove that. I don't know. My apologies if you were making a joke. I hate to come off as overly serious.

I think this discussion might hinge on how fat the human face is, whether it has small ears and small chin, certainly the face must be clean shaven, with a bald head .. and it would help if it were jaundiced, or in the case of the green face, perhaps a severe liver problem, but in that case I doubt if it would be wearing such a big smile. Personally, I'm offended that none of the apod smiley faces have unibrows like mine .. outright discrimination I would say.

[Drabkikker]

I think this new entry at atoptics.co.uk settles the discussion for good.

[neufer]

I think this new entry at atoptics.co.uk settles the discussion for good.

It's not the color of the "apparition" but rather its distinctive shape.

Are the shadowing effects caused by the outside of the plane or the inside of the plane?