[orbsycli]

Earlier today I stood on an ageing dock on the gulf of mexico. a question i could not answer struck me as i just stood there.
to my eyes, i can see the curvature of the earth. is this just an illusion? or can you really see a slight curve of the earth?

[Turtle]

Indeed you saw it. The first known recorded estimate of Earth's diameter was prompted by watching ships disapear over the horizon. I forget the ancient guy's name who compared the shadow cast by the Sun at zenith in one location, to the shadow cast at the same time in another location, & so derived the curvature/diameter /circumference of Earth.
___I have heard that under the clearest conditions, one can see from sea level, 17 miles to the horizon before Earth curvature puts objects out of sight.

[orbsycli]

Oh whoa, i wasn't even talking about outwards, i meant horizontaly. that's amazing though.

[orbsycli]

i suppose if you can see 17 miles outwards, if you take a look at the span of the horizon, it is definitely more than 17 miles across. therefore, you must be able to see earth's curve across, and is indeed not an illusion.

[alexander]

well, here is a guess:
if we take the circomference of earth at the equator (24,902)
360 degrees and 17 miles, i hope we can figure out the corver of the earth over 17 miles (at eqator) (360 / 24,902) *17 = 0.245763392 (googled it)
so you were looking at about .3 degree curver over 17 miles of the horison, you could have seen that it is not a straight line
actually from having an experience of sitting on the coast of the gulf looking at the horison, you really can see the curve of the earth, its definately a pretty cool feeling

[mne]

if you were standing on the shore in long beach, 26 miles to catalina, and another person your height was looking back at you, how tall would you have to be to see each other in the eyes. how many miles are you from each other when you must be one foot taller?