Maths Question(s) - Horizon

[drivin_me_nuts]

How much further out to sea would you be able to see... if you stood on a 100ft hill? than if you stood on a beach at sea level?

I know there is a formula for this, but could someone with less fluff and more grey matter between their ears please enlighten me ..

Cheers

(Also... how far off the earth's surface do you have to be to see the whole of the earth.. as in a big circle, because clearly you could not see the whole of the earth at any one time....unless you were god in which case the earth is just a microscopic peice of flotsam and jetsom floating in your morning's chicken broth..)

Cheers .. again

[TheEnd]

numero uno

For an observer standing on the ground with h = 1.70 m (average eye-level height), the horizon is at a distance of 4.7 km.
For an observer standing on a hill or tower of 100 m in height, the horizon is at a distance of 36 km.

http://en.wikipedia.org/wiki/Horizon

and part b,

well, thats quite tricky, as to truely see the exact circumference of the earth, you'd need to be an infite distance away. Think of it as the further you go away from it, the wider the horizon appears, and about 100 miles away, you'd see quite a lot, but still not the exact mm perfect line.

[nlldavies]

http://www.ringbell.co.uk/info/hdist.htm

[John_S4x4]

As for the seeing the earth as a whole, if we say the that the diameter of the earth is 7926 miles wide and the average human being has a field of view of 120 degrees, then a bit of trig gives you 4576 miles. Then subtract half of 7926 miles to give you 613 miles away.