How far can we 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 – eg 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 cloud gets 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 2.25 million light years away.

Answered by Luis Villazon, How It Works contributor.

  • Real AF/Sub-Zero

    2.6 million light-years

  • Cathy

    Do we actually see Andromeda, or do we see the light that is being emitted from it?

  • Weston Liveit

    Cathy, I have wondered about that as well. It is more like the light from the Andromeda Galaxy have traveled through time and because it shines brightly we can see. We do not see it because we have such great vision. If we did, then we would be able to see it during the day as well. But getting back to the question of how far we can really see unobstructed, I think a related question is how well we can make out objects from a distance.