Mountain Light

Alpenglow is a beautiful phenomenon associated with mountains that light up reddish-pink right before sunrise or after sunset.  John Muir once said, “Next to the light of the dawn on the high mountain tops, the alpenglow is the most impressive of all terrestrial manifestations of God.”  There is conflicting information on the Internet as to whether alpenglow results only from indirect light or whether it is also from direct light.  I can’t say for certain but my personal opinion is that alpenglow only occurs from indirect light and it doesn’t happen all the time.  It occurs when there are sufficient airborne particles (like snow, water or ice) in the atmosphere to reflect the sunlight down onto the landscape.  When in doubt, I simply refer to it as mountain light.

Last light of the day on the Sierra Nevadas from Glacier Point in Yosemite National Park (Doug Oglesby)

Last light of the day on the Sierra Nevadas from Glacier Point in Yosemite National Park

Direct light shining on mountains is frequently attributed to alpenglow when it’s not – it’s just beautiful mountain light.  Reddish-pink light on mountains is commonly mistaken for alpenglow when the sun isn’t visible to us as we stand at the mountain’s base. Under this scenario, the mountains are still bathed in a glorious reddish-pink light but only because the sun is able to directly hit the tall mountain peaks.  The image above is an example of this.  The sun is below the horizon but shining directly on the mountains, bathing it in soft reddish-pink light (i.e., this is not alpenglow).

First light shining on the Sierra Nevadas from Mono Lake (Doug Oglesby)

First light shining on the Sierra Nevadas from Mono Lake.

Regardless of whether you believe alpenglow results from indirect or direct light, what isn’t in dispute is that the reddish-pink color results from a very low angle of the sun.  When the sun is near the horizon its light travels low through the atmosphere for a lengthy period of time.  This is a much longer period of time than if it was directly overhead during the middle of the day.  The longer sunlight travels through the atmosphere the redder it becomes.  This happens because of light scattering – violet and blue light scatters more than orange and red light. The longer light travels through the atmosphere, the more the violet and blue light disperses, making the light visible to us more red.  It happens gradually as the sun rises and sets.

At sunrise and sunset the light will have to travel longer through the atmosphere than at any other time of day.  As a result, more red light is left at the end of its journey (in this case “the end” is where you are standing).  The cleaner the air and the higher the peaks, the more vibrant the color and memorable the experience.  There is nothing like a sunrise or sunset in the mountains.  Mountain light is my all-time favorite event.

At sunrise, this reddish-pink light slowly creeps down mountain peaks until just after the sun rises and the light turns golden.  We have now entered the fabled “golden hour” or “magic hour” that photographers love to talk about.  As the sun continues to rise more of the violet and blue light is retained, the golden hues vanish and we are left with more yellow and brighter sunlight.  This is the fabled “crappy light” that causes photographers like me to go home!  The process is, of course, reversed during sunset.  Mountains tend to show vibrant and intense color because, generally speaking, the air is so clean.  Contrary to popular opinion, pollution and haze are the enemies of vibrant colors.

Early light on Mount Whitney from the Alabama Hills

Early light on Mount Whitney from the Alabama Hills.

Now, I cannot tell you definitively which of my images are alpenglow (if any).  But, I firmly believe the first image from Glacier Point in Yosemite of Half Dome is alpenglow; the sun dropped below the horizon and all direct light disappeared. I nearly packed up my gear.  Suddenly Half Dome glowed red/pink.  It lasted for just a moment.  It was an astonishing experience.  So, the next time you are in the mountains, don’t leave right after the sun drops below the horizon.  You just might get treated with a memory to last a lifetime.

Sidebar: now, what about the clouds that light up in such an amazing orange, red or pink?  Why doesn’t that happen all the time whenever there are clouds overhead at sunrise or sunset?  The short answer is that it takes the “right” kinds of clouds for an amazing sunrise or sunset.  The “right” kinds of clouds are generally those that are high in the sky – altocumulus and cirrus.  For lower clouds (like stratus and stratocumulus) to light up it generally requires very clear air; this is most prevalent in the tropics – it’s seen quite a bit in Hawaii, for example. And, for the record, this is not alpenglow.  The sun is shining directly on the bottom of the clouds.

Sunrise in Joshua Tree N ational Park (Doug Oglesby)

Sunrise light on the mountains in Joshua Tree National Park.  This is the high desert – an elevation of approximately 4,400 feet.

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