How Dark is the Sky at the Summit of Mount Everest?

The sky at the summit of Mount Everest appears noticeably darker than it does at sea level. This phenomenon is due to two key factors: altitude and atmospheric thickness, both of which significantly influence the scattering and absorption of sunlight. In this article, we will delve into the science behind why the sky at the summit of Mount Everest looks so dark and explore how this differs at lower altitudes.

Altitude and Atmospheric Thickness

At higher altitudes, such as the summit of Mount Everest, which sits at approximately 8,848 meters (29,029 feet), there is less atmospheric mass above you. This means there are fewer air molecules to scatter the sunlight, leading to a darker sky. The reduced atmospheric density also means that less light is scattered or absorbed by the air, resulting in a deep blue hue during the day. At heights above 3,000 to 3,500 meters, the atmospheric pressure drops significantly, which can be felt as a difference in how the sky looks.

Reduced Scattering of Sunlight

The phenomenon of Rayleigh scattering, where shorter wavelength light (such as blue and violet) is scattered more than longer wavelength light (such as red and orange), is less effective at high altitudes. This is known as atmospheric attenuation, which occurs when sunlight passes through the thinner atmosphere, resulting in more light reaching the ground and sky. Consequently, the sky at higher altitudes appears darker and more blue compared to lower elevations.

Comparison with Altitude in Airplanes

Even at the cruising altitude of a commercial airliner, the sky can appear darker than it does at sea level. People who have experienced this phenomenon often note that the sky seems more blue and less white from a higher altitude. This is because the effect of Rayleigh scattering is more pronounced at these heights, leading to a clearer and darker sky. For instance, air travelers frequently report that the sky at high altitudes can appear almost black, especially when contrasted with the white clouds and surfaces below.

Photos and Elevations

To illustrate this phenomenon, consider photos taken from different elevations. For example, a photograph taken near Everest Basecamp at an altitude of 5,250 meters (17,222 feet) would show a distinctly darker and more indigo-colored sky when compared to lower elevations. The sky at the summit of Mount Everest, at 8,848 meters (29,029 feet), can appear almost black, even during midday, due to the reduced scattering and absorption of sunlight. This is because the air is thinner and contains fewer particles that can scatter light.

Visual Evidence from Ski Resorts

For those who have experienced high altitudes without reaching the summit of Mount Everest, visual evidence is available from ski resorts at varying elevations. Websites such as Tignes France and Vail Colorado offer webcam views from different altitudes, allowing viewers to compare the clarity and color of the sky. These webcam images further support the observation that the higher the altitude, the darker the sky appears to be.

Conclusion

The sky at the summit of Mount Everest is considerably darker than it is at sea level or even at common skiing altitudes, due to the effects of altitude and atmospheric thickness. This phenomenon is not only fascinating from a scientific perspective but also provides tangible proof of how our perception of the sky can be significantly affected by our elevation. The next time you catch a glimpse of the sky from an airplane or from the top of a ski resort, take a moment to appreciate the stark contrast between the darkness above and the clarity of the lower atmosphere.