This image of Paranal Observatory shows skies that regularly display a myriad of colours and astronomical sights, from the plane of the Milky Way shining brightly overhead to the orange-hued speck of Mars (left), the starry constellations of Scorpius and Orion, and the magenta splash of the Carina Nebula (upper middle). Image credit: Y. Beletsky (LCO)/ESO.

Earth’s night skies aren’t black at all

The darkness we see from Earth can never be 100% dark.

“All I want is blackness. Blackness and silence.” -Sylvia Plath

If you take a look at the night sky from an extremely dark sky location, away from all the city lights, street lights, squid fisheries and other sources of human-caused light pollution, you’ll be treated to one of nature’s most spectacular sights: the view of outer space itself. We think of space as the blackest thing there is, as though it’s the absence of all forms of light whatsoever. As far as visible light goes, the Hubble space telescope represents our best view into the dark, distant Universe. The longest it ever looked at any one region of space was for a total of 23 days. When it did that, here’s what it found.

The full UV-visible-IR composite of the XDF; the greatest image ever released of the distant Universe. Image credit: NASA, ESA, H. Teplitz and M. Rafelski (IPAC/Caltech), A. Koekemoer (STScI), R. Windhorst (Arizona State University), and Z. Levay (STScI).

Sure, you might look at an image like this and see the brilliant galaxies and their stars from so long ago, and think that if only we could see even farther, perhaps the entire sky would be filled in with sources of light. But that’s not the case at all! The Universe is limited in terms of the amount of “stuff” observable to us, as we can only see as far back as the Big Bang and as light has traveled in the 13.8 billion years…