In the sky
|Q.39:||How far away is the horizon (neglecting refraction)?|
This is, of course, question 14, “reloaded,” and it leads naturally to question 40.
From figure 39.1, we can approximate the distance x from an observer at O, a height h above sea level to the horizon at T. This neglects the effect of atmospheric refraction, of course, but since that increases the effective “distance” by about 9% (see the article by French) this result represents a lower bound. Also ignored is the limiting effect of haze. By Pythagoras' theorem, if the distance OT= x, then
since h << R. A useful rule of thumb version is easily established if we suppose ...