JACKSON, Wyo. — The reddish-pink light reflecting off of the Tetons at sunrise or sunset is a sight to behold during the winter season.
The National Park Service (NPS) describes why the phenomenon of alpenglow occurs during early morning and evening hours.
“During sunset or sunrise, light from the sun’s low angle in the sky takes a long path through the atmosphere,” the NPS posted to social media in 2022. “The atmosphere acts like a camera filter, filtering out blues and greens and leaving behind oranges, reds and yellows.”
According to the NPS, alpenglow is more visible during dry weather patterns.
“Although alpenglow can occur throughout the year, moisture can block sunlight and dilute colors,” said the NPS. “In dry areas and in the winter, there is often less moisture in the atmosphere, which then causes more brilliant colors.”
There is some debate over whether alpenglow is indirect light or direct light. To a person standing in a valley surrounded by mountains, a setting sun might look like it’s below the horizon, but really the sun remains above the horizon, casting its rays (direct light).
On the other hand, some feel that true alpenglow occurs when the sun is below the horizon for both the person in the valley and the top of the mountain. The red wavelengths are hitting the mountaintops after they are reflected off of elements in the atmosphere (indirect light).
Editor’s note: This story runs annually.
