Labels	Values	formula
R, radius of Earth (miles)	3963
D, distance from observer (miles)	60
α, angle to observer (radians)	0.015140045	D / R
A	3962.545807	R ∙ cos(α)
B	59.99770782	R ∙ sin(α)
C	0.454192687	R - A
E	59.99942695	sqrt(B²+C²)
F	29.99971347	E / 2
G	3962.88645	sqrt(R²-F²)
H	0.113549798	R - G
H in feet	599.5429355	H x 5280 ft/mi
Calculate the height of the effective barrier between observer and object under observation, created by the
curvature of the Earth, as a function of the distance between observer and object under observation.
I.e., calculate the maximum height difference between a straight line and a curve which follows the curvature
of the Earth.
The fundamental deficiency in this approach is the assumption that Earth has no atmosphere.
In the real world, the Earth's atmosphere acts as a lens, which refracts light. Depending
on atmospheric conditions, it is often possible for things beneath the horizon to appear at
the horizon, or even above the horizon. Here are a couple of very good web pages on this topic:
http://www-rohan.sdsu.edu/~aty/explain/atmos_refr/horizon.html
http://www-rohan.sdsu.edu/~aty/explain/atmos_refr/altitudes.html

This is an exported Excel spreadsheet. You can load it directly into
Microsoft Excel 2003 or later, or another compatible spreadsheet
program, such as Kingsoft WPS Office "Spreadsheets" (but not
OpenOffice), to view (or change) the formulae & values.

Dave Burton

www.sealevel.info

30 April, 2016