{"id":29605,"date":"2022-02-11T10:05:26","date_gmt":"2022-02-11T10:05:26","guid":{"rendered":"https:\/\/www.skyatnightmagazine.com\/?p=104596"},"modified":"2022-02-11T10:23:13","modified_gmt":"2022-02-11T10:23:13","slug":"how-dark-is-space","status":"publish","type":"rss_feed","link":"https:\/\/c01.purpledshub.com\/bbcskyatnight\/rss_feed\/how-dark-is-space\/","title":{"rendered":"How dark is space?"},"content":{"rendered":"

<\/p>

By Lewis Dartnell\n \t\t<\/p>

Published: Friday, 11 February 2022 at 12:00 am<\/p>

\n\n

Space is dark. That much is obvious to anyone. Look up on a clear night in the middle of winter and all that appears to be surrounding the stars is inky blackness.<\/p>\n

At the centre of our Solar System lies the Sun, which casts brilliant light and warmth onto the planets of the Solar System<\/a>.<\/p>\n

And, of course, there are all the other billions of stars whose light should surely be illuminating the night sky. Why hasn\u2019t their light reached us yet?<\/p>\n

\""The\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
Credit: ESO\/C. Malin<\/span><\/figcaption><\/div>\n

This is an age-old problem that astronomers refer to as Olbers\u2019 paradox, named after the German astronomer Heinrich Olbers (although many earlier astronomers like Johannes Kepler<\/a> have advanced the notion).<\/p>\n

No-one has sufficiently answered the problem of Olbers\u2019 paradox. It could be that stardust<\/a> is obscuring star light from the human eye; perhaps the Universe is still too young for all the starlight to have reached us.<\/p>\n

Or could it be that light from distant stars has been red-shifted<\/a> by the expansion of the Universe?<\/p>\n

But let\u2019s ignore Olbers\u2019 paradox for a moment.<\/p>\n

How dark is outer space beyond the Solar System? Would two spaceships flying together in the deep, dark Universe be able to see each other?<\/p>\n

\""Two\"<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>
Could two spaceships travelling in deep dark space see each other? Credit: Sylphe_7 \/ Getty Images<\/span><\/figcaption><\/div>\n

It\u2019s difficult to know for sure, but there are some inferences that can be made.<\/p>\n

One astronomer attempted to answer this by collating the individual brightnesses of known stars and galaxies<\/a> listed in catalogues, and in doing that the answer converges at a visual magnitude of \u20136.5, or 0.3% as bright as a full Moon<\/a>.<\/span><\/p>\n

Obviously, this average brightness would not stay the same as you journey through the Galaxy: near the galactic centre, far more stars are packed closely together.<\/span><\/p>\n

Now, whether two space ships could see each other solely by this dim starlight would depend on the shininess of the spacecraft (mirrored or matt black) and whether they carried a telescope on board.<\/span><\/p>\n

But think how difficult it is to see anything on a dark, moonless night on Earth.<\/span><\/p>\n

Ocean-going ships passing within just a few miles would struggle to see each other if it weren\u2019t for their navigational lights.<\/span><\/p>\n

This article originally appeared in the March 2010 issue of <\/strong><\/em>BBC Sky at Night Magazine<\/strong>.<\/strong><\/em><\/p><\/body><\/html>\n

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