Earth’s darkest night skies aren’t truly black at all (Synopsis)
“All I want is blackness. Blackness and silence.” -Sylvia Plath
Even on the darkest night skies from the most pristine locations on Earth, the night sky is never truly dark. Not even if you look away from the plane of the galaxy, on a moonless night, between the stars and away from any human-made or nature-made sources of illumination. Unlike the views that a telescope like Hubble can get from space, nothing on Earth is ever devoid of photons that have their origin in starlight.
The full UV-visible-IR composite of the XDF; the greatest image ever released of the distant Universe. Every galaxy shown here will eventually accelerate away from us at greater than the speed of light, thanks to dark energy. Image credit: NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI).
That’s because, unlike from space, even the highest-altitude, lowest-turbulence and most pristine locations on Earth still have to contend with our atmosphere. This atmosphere still reflects and refracts light — even if it’s starlight, not sunlight — and exhibits the effect of airglow due to air circulation and interactions with the Sun during the day.
One of the few galaxies — the Large Magellanic Cloud — as visible from Earth. The faint background light comes from Earth’s atmosphere. Image credit: Y. Beletsky (LCO)/ESO.