Thread: Level Ground - Oil Checks.

Only place I have had to land and ask where I was was in PNG!

Originally Posted by Eevo

told you the earth was flat

Apparently it's not flat. Mind you, my eyes are so bad I couldn't tell anyway...

The Earth has a radius of approximately 3965 miles. Using the Pythagorean theorem, that calculates to an average curvature of 7.98 inches per mile or approximately 8 inches per mile (squared). The distance to the horizon in miles from height of an observer is approximately equal to 1.23 times the square root of the height in feet. For example 1.23 times the square root of 8 divided by 12 equals 1 mile. Inversely given the horizon distance in miles, the height in feet required to be visible equals the distance in miles squared divided by 1.513. The second example above concerning the Moon rising over a distant range also requires some topographic map calculations using the tan trigonometric function. Thus if a peak rises up 1844 feet at a distance of 10.0 miles or 52,800 feet, it will form an angle of 2 degrees with a theoretical flat horizon. The tan is 1844/52800=0.0349 or 2 degrees. However due to the Earth's curvature, it would appear as though it was only 1778 feet tall with the lowest 66 feet below the horizon.
Disregarding refraction, on a perfectly flat plain like the Bonneville Salt Flats in Utah, if one's eyes are 9 inches above the ground, one would be able to see at night a flashlight one mile distant laying on the surface but not if one lowers their eyes to 7 inches. For example per the above diagram, that might be between the tangent point and Object B.

David Senesac Visual Line of Sight Calculations dependent on Earth's Curvature