Opposition effect from the air

Last updated on September 16, 2023

The Opposition Effect from the Air: Exploring the Phenomenon

Have you ever noticed a subtle glow drifting across the landscape while flying in an airplane? This fascinating optical phenomenon is known as the Opposition Effect. In this article, we will delve into the details of this intriguing occurrence and explore its characteristics.

When observing the Opposition Effect from the air, one may notice a yellow spot that appears to follow the plane. This glow gradually vanishes as the aircraft flies from east to west. Interestingly, this effect occurs even when there is no water or ice crystals in the air, but rather just dust and sand particles.

The Opposition Effect is characterized by a subtle glow observed towards the antisolar point. This glow is slightly yellow due to the absence of shadows. Shadows, on the other hand, typically appear bluish as they are primarily illuminated by blue skylight.

While the glory and heiligenschein are other types of antisolar brightenings, they require the presence of water droplets. However, in a desert setting, an afternoon glow often serves as a reliable indicator that the opposition effect is at play.

Now that we have explored the basics of the Opposition Effect, let's delve deeper into its underlying mechanisms:

1. Explanation: The Opposition Effect occurs when light is scattered backward towards the observer, resulting in an enhanced brightness of the illuminated surface.
2. Backscatter: The backscattering of light is responsible for the opposition effect. This occurs when light particles are scattered in the opposite direction of their original path.
3. Surface Roughness: The presence of dust and sand particles in the air contributes to surface roughness. These particles can effectively scatter light back towards the observer, intensifying the opposition effect.
4. Absence of Shadows: The absence of shadows in the opposition effect is due to the direct illumination of the surface by light particles scattered in the backward direction.
5. Yellow Glow: The yellow hue observed in the opposition effect is a result of the absence of shadows and the specific scattering properties of the dust and sand particles present in the air.
6. Directional Dependency: The opposition effect is most pronounced when observing a surface directly opposite the light source, such as when flying from east to west.

It's important to note that the opposition effect can be observed not only from the air but also from the ground. In fact, this phenomenon has been observed in various natural settings, including deserts, snow-covered landscapes, and even on celestial bodies like the Moon.

In conclusion, the Opposition Effect is a captivating atmospheric optics phenomenon that manifests as a subtle glow observed towards the antisolar point. While it typically requires the presence of water droplets, the presence of dust and sand particles can also give rise to this intriguing optical phenomenon. Whether witnessed from an airplane or on the ground, the opposition effect never fails to captivate our curiosity and remind us of the wonders of our atmosphere.

Opposition Effect glow, Uzbekistan. Photograph by Eva Seidenfaden (Atmospheric optics site) - " .. taken on the 17th of September about half an hour after takeoff from Tashkent at 15.30 local time.

The yellow spot kept following the plane, but eventually vanished behind it because we were flying from the east to the west.

There was no water in the air, nor ice crystals, just dust and sand."

Look carefully towards the antisolar point for this very subtle glow drifting across the landscape as the aircraft flies onwards.

It is slightly yellow because of the absence of shadows. Shadows are bluish because they are lit predominantly by blue skylight.

The glory and heiligenschein are other antisolar brightenings but they need water droplets. An afternoon glow in a desert is a fairly sure sign that the opposition effect is operating.

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Reference Atmospheric Optics

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