# On open sea how far away is the visible horizon?

Or from the coast at ground level how far away is the horizon when looking out to sea?
19:08 Thu 05th Jul 2012
 Graham-W With d in miles and h in feet, d=approx 1.22*sqrt{h} Examples, assuming no refraction: For an observer on the ground with eye level at h = 5 ft 7 in (5.583 ft), the horizon is at a distance of 2.9 miles (4.7 km). 20:36 Thu 05th Jul 2012 Go To Best Answer

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 i think i remember reading once, a long time ago - it is about 19 miles but i may be a little out. 19:10 Thu 05th Jul 2012 I heard 18 miles - so somewhere near I pressume - unless you're in the crows nest 19:11 Thu 05th Jul 2012 if i remember correctly , if your six feet tall its about two miles (but i could be wrong !) 19:12 Thu 05th Jul 2012 take distance of eyes above sea-level, multiply by 1.6, and take square root to get distance in miles 19:12 Thu 05th Jul 2012 should have said that distance of eyes above sea-level is in feet 19:13 Thu 05th Jul 2012 http://en.wikipedia.org/wiki/Horizon 5' 7" = 2.9 miles 20:02 Thu 05th Jul 2012 There isn't an exact answer. It depends in the tide at the time (yes there are tides in the middle of the ocean) 20:06 Thu 05th Jul 2012 There seems to be a variety of answers. I was once told it was 7 miles. 20:32 Thu 05th Jul 2012 With d in miles and h in feet, d=approx 1.22*sqrt{h} Examples, assuming no refraction: For an observer on the ground with eye level at h = 5 ft 7 in (5.583 ft), the horizon is at a distance of 2.9 miles (4.7 km). 20:36 Thu 05th Jul 2012 03:51 Fri 06th Jul 2012 -- answer removed -- This was on QI - but I can't remember the answer. I think it was a lot less than expected. 10:23 Fri 06th Jul 2012 3 ABers agreeing (Howard, Graham and Mibs), it must be the right answer and it is! 19:01 Fri 06th Jul 2012 With or without the fog? 19:07 Fri 06th Jul 2012 Daisy, the horizon is still there with or without the fog and even at night. That is why the water doesn't run over the edge. :-) 19:10 Fri 06th Jul 2012 If there is a swell, the distance to the horizon must keep changing dramatically. 19:18 Fri 06th Jul 2012 ^^ I think the assumption is that one stands at the water edge. It can never be calculated accurately because of the moon's gravition, it bulges the sea at high tide and flattens it at low tide. 23:00 Fri 06th Jul 2012 Also the earth is not spherical which will have an effect as well. 23:02 Fri 06th Jul 2012

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