Talk:Line of sight

Horizon

If a 6' person is standing at sea level, assuming a clear day, how far can one see an object at sea level, before the curvature of the earth obstructs the visibility?

http://www.boatsafe.com/tools/horizon.htm (JavaScript required) lets you enter height in feet or meters and get the distance to the horizon. According to that site, someone with their eye height at exactly 6 feet above the surface could see 3.297 (land) miles, which is 2.863 nautical miles or 5.306 km. If it was a 6 foot person and their eyes were 6 inches down their head, the eyes would be at 5.5 feet, so it would be more like 3.157 miles. According to http://www.theanswerbank.co.uk/Science/Question190575.html the formula to calculate the horizon from a height away from circle is

{\sqrt {h+2rh}}

where

h

is the height and

r

is the radius of the circle. The Earth's average radius is 20,908,120 feet, so if you're 6 feet off the surface, you get

{\sqrt {6+2(20908120)(6)}}

which is 15840 feet, really close to 3 miles if you use straight line of sight from the eye to the horizon. It's a little bit more if you're measuring how far across the curved Earth it is if you wanted to travel to it. For metric folks using meters, that's

{\sqrt {1.8288+2(6372795)(1.8288)}}

or 4827.0 meters. --Closeapple 08:10, 23 January 2006 (UTC)[reply]

To calculate when one will see a distant object over the horizon: http://scubageek.com/articles/wwwhorizon.html --Closeapple 08:41, 23 January 2006 (UTC)[reply]