A worldwide atmospheric glow
Airglow looks similar to the aurorae, but can be seen all over the world. Light from cities and towns often prevents us from seeing features in the night sky, which is never completely dark.
As well as escaping light pollution, you need your eyes to have adapted to the dark to allow them to see the faint light of airglow. Like the aurorae, the light, and its colour, are much more vivid in long-exposure photography.
Jesper Grønne who made the first two videos in this post, explained to the Danish weather service Danmarks Meteorologiske Institut that he managed to capture the elusive light show on the west coast of the country.
Although Denmark can also experience the aurora borealis, or Northern Lights, the greenish light of airglow is created differently.
Grønne explains: “Airglow has a chemical origin that is different from the way the northern lights occur. During the day, the sunlight causes air molecules to split up, and when the molecules come back together at night, they emit the faint greenish, yellowish or reddish light – ambient glow that means the sky is never completely black. In contrast to the northern lights, seen only in polar neighboring regions can ‘airglow’ appear anywhere on Earth. “
Grønne’s website includes images of a wide range of interesting meteorological phenomena, such as sprites, noctilucent clouds, and the “green flash” at sunset.
Airglow can also be seen clearly from space.
This NASA image, taken on board the International Space Station in September 2011 shows the airglow from the Earth’s atmosphere, just beyond the Soyuz and Progress vehicles docked on the station.
Although airglow is much more obvious from space, it was correctly identified long before the space age. Swedish physicist Anders Ångström discovered during his study of the aurorae that there were some emissions in the sky even when there was no auroral display. Later, in the 1920s and early 1930s, scientists identified the cause of airglow, and showed that oxygen and sodium were among the molecules creating the light. It can also be called “permanent aurora” or “earthlight”.