Talk:Alpenglow

I feel it is unnessisary to state when the sun sets in the west, as the sun always sets in the west. Could someone clearify this?

I concur. Although I must point out that technically, we only perceive the sun as "setting" in the west. With the exception of some of the polar regions, I believe that all areas have a "west-setting" sun. Therefore, I'm taking the "sets in the west" portion out of the article. Flag-Waving American Patriot 23:29, 6 June 2007 (UTC)

FYI - other sources include sunrise light 68.96.98.142 21:08, 10 September 2007 (UTC)

Sorry, I beg to differ. Alpenglow occurs when the sun's rays are diffracted through the atmosphere when the light is tangential to the earth's surface. You can watch a progression of colors of the rainbow as the sun sets. It is a direct illumination phenomenon, not indirect as noted on the main page. The Golden Hour and Alpenglow are one and the same. To say that Alpenglow occurs after the sun goes down is like stating that you can break up a ray of light using a prism, without shining the ray of light. Alpenglow is a direct illumination phenomenon. The colors of the Golden hour are just part of the rainbow of light, when the atmosphere is diffracted through the atmosphere like a prism. If you watch the Golden Hour on a white glacier you can actually see the progression of colors of the rainbow.Hmarin (talk) 23:15, 7 March 2010 (UTC)

As someone once said, if you stand on a mountaintop bathed in alpenglow, you will see the sun above the horizon. Alpenglow is a phenomenon of DIRECT SUNLIGHT, not indirect.Hmarin (talk) 10:08, 14 March 2010 (UTC)

Yes, many people use "alpenglow" to mean direct illumination from the setting or rising sun. But the word means more than that:

“ High, snow-covered mountains glow yellowish orange when lit up by the low sun. Perhaps 30 minutes later after the sun has set, the same mountains radiate a lovely purple which seems to brighten as their surroundings fade. This mountain glow is called the alpenglow. ” — David K. Lynch and William Charles Livingston, Color and Light in Nature (2001) page 41

It seems that they include the pre-sunset golden light as an early stage of alpenglow, but the purple alpenglow occurs when the sun is well below the horizon, and is too diffuse to cast shadows. Palpable (talk) 08:19, 7 April 2010 (UTC)

Isn't alpenglow just another name for either the Belt of Venus (when purple) or the golden hour (when golden) but specific to snow-capped mountains? Does this term need its own page? And if so, should it be mentioned as having no clear definition, but appears to describe either the Belt of Venus or the golden hour alternately, but as it appears from snow-capped mountains? Or am I missing something completely unique about it? 75.22.189.234 (talk) 08:22, 29 May 2011 (UTC)

Lots of issues here

There are several issues here on the talk page, as well as in the article itself - I'm going to try to explain these effects here before I make any edits. First, the Golden Hour is a photographic term describing the nice, warm light you get during a brief period (an hour or so) while the sun is STILL UP. The light is reddish due to Rayleigh Scattering, and it makes for great pictures. There is no relation between the Golden Hour and Alpenglow, or with the Belt of Venus. It's just a great time to take pictures because of the warm light available due to Rayleigh scattering.

Alpenglow is used to refer to the light which is available while the sun is below the horizon (at twilight), despite the comments by Hmarin above (please see atmospheric refraction). This light is both Rayleigh scattered causing its redness, and it is also refracted (bent) and reflected (scattered) off the atmosphere. It is not the atmospheric refraction which is responsible for any dispersion of frequencies as would be the case in a prism (the index of refraction of air is not high enough to appreciably split apart the frequencies - it is about 1.0 in air vs. 1.5 in glass). And hence, there is no rainbow-based progression of colors on the horizon opposite the sun, nor does the sun show varied colors along its disk during sunset and sunrise (refractive frequency dispersion due to air is insignificant). Perhaps this was confused with several phenomena, the dark segment and the belt of venus being responsible for possibly two colors out of a perceived rainbow.. I'm not sure, but none of that is physically correct.

Now, all light is refracted at the horizon due to the long path through the atmosphere at that elevation, and it is refracted roughly by 0.5 degrees. So when you see the reddish sun at sunset, the sun has already set, but you can still see it due to refraction (see atmospheric refraction). This would still be "direct" sunlight, because you can see it coming at you even though it has been refracted. I believe that a strict usage of the term alpenglow, in contrast, is due to light from the sun while it is (visibly) below the horizon, or during twilight. This light has been refracted due to its low elevation in the sky, it is also reddish due to Rayleigh Scattering, but it is coming from a sun which is visibly below the horizon, and being refracted enough to still shine on the atmosphere above you, and it reflects off the particles in the atmosphere. So this light is also reflected (scattered) off the atmosphere, in addition to having been refracted and reddened. And this is what casts a reddish tone over the scene. It normally doesn't bounce off of anything if you aren't next to a nice huge, reflective mountain, and so the common usage refers to mountains in alpenglow. But this light would also illuminate particles in the atmosphere on the far horizon - this light would then be seen as "backscattered" (versus "forward scattered", or any other angle of scattering). So the description of backscattering is certainly included in all of this, but it's not the only feature (alpenglow is not solely due to backscattering on the far horizon).

The problem is that the common usage of the term seems to include the case where "direct" sunlight is cast on mountains, such as in this picture [1]. This seems to be direct, but reddish, sunlight on the peaks (in other words, if you were on the peak, you could see the sun on the horizon as Hmarin noted, but you can't see the sun because you are still below the line of shadow in this picture). However, if you look at this picture [2], you will not find a line of shadow. The entire scene is bathed in a reddish light while the sun is still below the horizon. Note that this is not a "glowing band" on the "horizon opposite to the sun" as the article claims, but I do like the last sentence in the first paragraph - that seems to make it more clear that we are talking about the light available, and that it doesn't really matter what it is illuminating. It could be mountains, or it could be the atmosphere, or it could be you or me. I think a bit of the confusion stems from the part where we talk about the mountain tops being illuminated by a reddish light, and that makes people think that alpenglow is just when the mountain tops are getting direct sunlight, but you are not, simply due to the geometry of the situation. But before the "direct" sunlight hits the mountain tops, there is a reddish light available. And if you are next to a snowy mountain, it is easier to notice. THAT, as I understand it, is alpenglow.

But not to be too strict about things, I think the first picture and this one are both good examples of what people mean by alpenglow [3], although I think that the tops of these mountains are getting some direct (but very red) sunlight. Still, I think this is what is commonly understood as alpenglow, and I'd be in favor of changing the article to reflect how the usage is more broad than the strict definition. The picture used in the article of the Maroon Bells is a good example, and should be kept.. But other pictures can be shown where a red (but direct) light illuminates mountaintops, and it can be said that this type of situation is commonly known as an alpenglow as well. Here is a link to what I think is a good description of the effect: [4] and here are some great example pictures of alpenglow [5]. HappyDa (talk) 03:28, 30 April 2015 (UTC)

HappyDa, your explanations sounds good. I would agree that the article needs to be edited to reflect your ideas. I also think it would be helpful to find an image to use that shows how the whole mountain is bathed in light that comes from the light scattered thourghout the atmosphere. Dedwarmo (talk) 18:47, 29 May 2016 (UTC)

First colouring, second colouring

Hi everybody. I have a little problem (or better, a question) with the given explanations above and in the article itself. The article refers to the German word Alpenglühen which definitely means two different phases. In German these are called "Erste Färbung" and "Zweite Färbung" which means something like first and second colouring. What is described in the english article is only the second colouring. In German the effect of direct sunlight shortly before sunset and shortly after sunrise belongs to the first colouring of the alpenglow. Now my question is: Shouldn't it be the same in English or do you really define the alpenglow differently? At least you exclude the first colouring explicitly in the article (cit.: "true alpenglow is not direct sunlight and is only visible after sunset or before sunrise"). Perhaps even the named reference (https://digital-photography-school.com/what-is-alpenglow/) is wrong? German printed dictionaries name both effects, the one before sunset (after sunrise), and the one after sunset (and before sunrise). So did the english people redefine the alpenglow differently from the original Alpenglühen? --Quadratur (talk) 13:35, 26 March 2019 (UTC)

The English language reference I have is from a book on atmospheric optics and favors the indirect lighting definition (direct lighting being so common that it is not a distinct phenomenon). I like the distinction you describe in German and it would be great to add it to the article if you can find a citation. The important thing from my perspective is for readers to understand that the indirect illumination is a distinct phenomenon; many people using the term "alpenglow" in English have only seen the "Erste Färbung". Palpable (talk) 23:27, 8 May 2022 (UTC)