Weather News

Why the night sky is never completely dark

Ben Domensino, Tuesday March 17, 2020 - 11:29 EDT

The dark side of the Earth is never completely dark because Earth's upper atmosphere glows at night.

Earlier this month, a photo taken from the International Space Station showed a faint ring of glowing amber light hovering high above Earth's surface.

Image: A photo of airglow taken from the International Space Station as it was passing over Kazakhstan on March 4th, 2020. Source: NASA/ISS

This luminous halo surrounding the planet was a phenomenon called airglow or atmospheric glow, which typically occurs when ultraviolet radiation from the sun energises molecules in the highest layer of Earth's atmosphere. Some of the molecules that are energised in the upper atmosphere during the day store this energy up and release it at night. The result of this reaction, which is called chemiluminescence, is a colourful layer of light that can be seen from the ground and from space.

While airglow occurs across the entire sky, it's easier to see near the horizon and through the light-enhancing effect of long-exposure photography. Under the right conditions and in the absence of light pollution, airglow can be seen with the naked eye.

Image: A photo of airglow taken from the International Space Station as it was passing over Australia on October 7th, 2018. Source: NASA/ISS

From the ground, airglow is sometimes mistaken for an aurora australis or aurora borealis, especially when it appears green. From space, the phenomenon is not uncommon in night-time photography captured from the International Space Station.

More breaking news

Sydney Morning Herald
ABC News
9News
News Limited

Display Your Local Weather

Weather News

Strong winds lash the southeast

13:15 EDT

A vigorous cold front has swept through parts of the southeast, bringing wind gusts in excess of 100km/h to some exposed and elevated parts.

When it rains, it pours over NSW

13:07 EDT

Parts of New South Wales have recorded their best daily April rainfall in decades, as a strong cold front and trough sweeped over the state overnight.

Sunflowers brighten up the Liverpool Plains countryside after years of drought

10:41 EDT

From dry and dusty paddocks an increasingly rare crop is flowering on the New South Wales Liverpool Plains, standing as a symbol of recovery from an intense one-in-100-year drought.