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# Distance to the horizon...

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If I were standing on a hill 100 meters above sea level, how far could I see on a very clear day? Or, what is the distance to the horizon? Thanks for help.

Guest Mar 8, 2017
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The radius of the Earth   ≈ 6371 km

And 100m = .1 km

The radius of the Earth plus the hill height will serve as the hypotenuse of a right triangle.....and the radius of the Earth will serve as one leg of this right triangle.

And the distance from the top of the hill to the horizon  will be the other leg of the right triangle.....and this distance, in km, will be given by :

√ [ ( 6371 + .1)^2  - 6371^2 ]   ≈ 35.7 km

BTW - This is a rather fascinating topic.....this "formula" will not take into account atmospheric blurring, etc.....you can read more about this here:  https://en.wikipedia.org/wiki/Horizon

CPhill  Mar 9, 2017
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If you allow for atmospheric refraction, then the distance will be approx.=39 km.

Guest Mar 9, 2017
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Thanks, Guest....!!!!

CPhill  Mar 9, 2017