How to calculate distance to horizon...

[dogjones]

...assuming a completely smooth surface of the earth. What is the formula to calculate when my friend disappears over the horizon? I've googled but it only takes into account my height looking toward the horizon, but not the height of the object I'm looking at (as it gets further away.)

As I am no mathboy, please can you guys give me the concrete answer to:

My eye level = 6 feet
Friend's height = 6 feet

How far away until he completely disappears over the horizon?

Many thanks thinkers!

Dog

[dogjones]

Darn, forgot to ask also:

My eye level = 6 feet

How far is the horizon at the surface of the earth (assuming again perfectly smooth). Just so we can get the difference! Approx 2.8 miles I seem to read, but would be great if you guys could confirm.

Many thanks again.
D

[dogjones]

From experiments with bits of paper, pennies and beers, we all think the difference between post #1 and post#2 is double. (ie answer to post #2 is double the value of answer to post #1). But then again we are ignorami!

[Dan O.]

Horizon