Alpenglow - can it be from direct sunlight?

Been reading up on alpenglow and there is conflicting information as to what it is. What isn't in dispute is that it occurs just before sunrise and just after sunset and is a byproduct of a very low sun whose light has to travel a long way through the atmosphere, scattering the blue light and leaving the classic reddish-pink light. The conflict arises between those that say it is only from indirect light - the sun below the horizon reflecting off particles in the air and hitting the mountain peaks - and those that say it can be from direct light as well.  

I am no scientist so can only go off of what I read and interpret, which obviously introduces the opportunity for being wrong! That said, I don't understand how alpenglow could be from indirect light. Wouldn't indirect light cause the entire mountain range to light up? Why just the peak?  And why does the reddish-pink alpenglow travel down the mountain briefly before it turns golden? How could that happen if the light is being reflected from above? This makes me think alpenglow is from direct light only - light from the sun below the horizon that is able to reach the tallest peaks; and as it rises, the alpenglow then moves down the mountain peaks until the sun gets high enough where it becomes golden.   

Does anyone have an opinion on this?

Alpen glow is the reflection of indirect light off clouds onto the surface of a mountain at sunrise or sunset...this is different than just the pink one experiences at sunset.

If that is true then why isn't the entire mountain range (and the surrounding landscape for that matter) bathed in pink at the same time? Afterall, if it's indirect light bouncing off clouds then why is the pink only present on the peaks? I don't disagree with you; I just don't know so I'm asking questions. I've seen information that claims it's not just indirect light. For example, our very own Gary Crabbe claims that it can include direct light: http://photo.net/nature-photography-forum/00FRnS

The phenomena of alpenglow is the glow part, the light seems to stand out from the mountain, bathing it in warmth. Because it is indirect, the light seems flat with little shadow definition. It really doesn't happen very often (I live where I can see snow capped peaks across the horizon), but when it does, you will know the difference.

OK. So you are saying it's a unique phenomena, separate and distinct from the reddish-pink light on mountain peaks in the morning then. Does the entire mountain light up simultaneously then?

The cloud that the light is reflected from determines the size of the area where the glow will show.

Thanks, Mike. That is interesting.  I had assumed it would be very broad and not localized to a single cloud. Much to learn! If you have any photographs of alpenglow I would be extremely grateful if you would post one so I could compare it to what I've seen. I'm wondering if I have never seen it, confusing it with just a beautiful reddish-pink glow, intensified as a result of the clear air of the mountains.  One other question - do you see alpenglow "progress" down a mountain - i.e., will it move down a peak as the sun begins to ascend until direct light hits it?



It's frustrating that there is so little information on the Internet on this topic. I've done a fair amount of searching and the information is very limited, mostly individual blog posts from photographers that assert a specific opinion, and not from scientists (though the closest I've found is someone from the NOAA but he didn't speak directly about alpenglow).  Your information has given me more of a technical understanding of the phenomenon and helped my understanding. So, thank you!

Doug, think of Alpenglow as a few years ago sitting on the beach smoking a doobie at OB, watching the sun go down and the green flash presents itself and an "oh wow" moment has happened.

Don't get me started about the green flash! LOL. Or doobies at OB. HA HA.

Thanks, Tony.  I saw the Wikipedia post. Wikipedia also posts as its example image a heavily processed photograph, so I cannot trust that as a good example. Frankly, I have an inherent distrust of anything on Wikipedia. Anyone can post on it so I don't rely on it. 

Gary Crabbe has an interesting article on his blog about alpenglow, which refers to direct sunlight without using the actual words. On a forum post on another site he does mention direct light specifically as part of alpenglow (and links to it from his blog post). I've seen other posts indicating direct light can be alpenglow too. 

Adding to the confusion, some articles claiming that it's only from indirect light refer to it as only occurring before sunrise and after sunset (that being their only explanation as to it being indirect light).  Of course, sunrise and sunset means the sun is above the horizon. And, the highest peaks will (obviously) take on light while the sun is below the horizon (of course I'm referring to the horizon from the perspective of someone at the base of the mountain). Those articles don't rule that out, which is frustrating to me (actually it's just plain poor writing!). 

I'm probably overanalyzing this (I'm a very specific person!).

Here's another example claiming alpenglow includes direct light - this article from the NOAA (it was published in 1927).

What I really want is some scientist to pop up on this thread like some cyber jack-in-the-box and provide an explanation. Then, based on his credentials I can finally relax!  I just want to know! I'll probably never know for sure though...I'll just have to decide which articles to believe...Right now, I'm siding with Gary Crabbe but I find Mike O's posts in this thread compelling since he is speaking from first hand experience and explains a unique phenomenon. My head hurts. Could be the bourbon though...