What is the maximum distance the human eye can see if unobstructed?

Dust, water vapour and pollution in the air will rarely let you see more than 20 kilometres (12 miles), even on a clear day. Often, the curvature of the Earth gets in the way first. For example, at sea level, the horizon is only 4.8 kilometres (2.9 miles) away. On the top of Mt Everest, you could theoretically see for 339 kilometres (211 miles), but in practice clouds get in the way. For a truly unobstructed view, though, look up. On a clear night, you can see the Andromeda galaxy with the naked eye, which is 2.5 million light years away – that’s 24 quintillion kilometres (15 quintillion miles), in case you were wondering.


Answered by Luis Villazon

To feature in our Brain Dump section, send us your questions to howitworks@futurenet.com or message us on Facebook or Twitter


For more science and technology articles, pick up the latest copy of How It Works from all good retailers or from our website now. If you have a tablet or smartphone, you can also download the digital version onto your iOS or Android device. To make sure you never miss an issue of How It Works magazine, subscribe today!

You may also like...