# Prospect distance from the ground and line of sight distance between two observers

Calculates the prospect distance from height at observer and line of sight distance between two observers.

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Calculator below computes the prospect distance from height at observer and line of sight distance between two observers. Some theory is placed below the calculator.

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**Prospect distance**

As shown on piture, observer's view is limited by horizon - imaginary line where sky touches the earth. According to picture we can calculate distance to the horizon from Pythagoras theorem.

where R - is Earth radius, usually taken as 6378 kilometers.

Atmospheric refraction increases the prospect distance by over 6 percent.

The result formula is

Simplified formula, which can be deduced from above, is often used

, for nautical miles or

, for kilometers

**Line of sight**

As shown on picture, line of sight distance is simply addition of two prospect distances.

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