On Tue, 01 Jan 2008 18:19:29 +0100, Mxsmanic wrote:

Kyle Boatright writes:

Anyway, it probably took me 20 minutes to reach the tower and by the time I
reached it, it was well below my altitude, (which hadn't changed). After a
little thought, I realized that the curvature of the earth had resulted in
an illusion that the tower was extremely tall when viewed from a distance,
but was only 1000' AGl (or 1800' MSL) in reality.

The curvature of the planet won't do this; it makes things seem lower, not
higher, just as a tower behind a hill might not appear as tall as it does once
you reach the crest of the hill.

No. Pilots are accustomed to judging the altitude of other aircraft based on
whether it's above or below the horizon. This is great for collision avoidance,
but doesn't work at longer ranges. ANYTHING located at the viewer's horizon
will appear above the altitude of the observer, and it *is* due to the curvature
of the Earth. See:

http://www.wanttaja.com/los.jpg

Normally, though, details at such distances are obscured by haze.

Ron Wanttaja