<P> It is similarly possible to calculate how much of a distant object is visible above the horizon . Suppose an observer's eye is 10 metres above sea level, and he is watching a ship that is 20 km away . His horizon is: </P> <Dl> <Dd> 3.57 10 (\ displaystyle 3.57 (\ sqrt (10))) </Dd> </Dl> <Dd> 3.57 10 (\ displaystyle 3.57 (\ sqrt (10))) </Dd> <P> kilometres from him, which comes to about 11.3 kilometres away . The ship is a further 8.7 km away . The height of a point on the ship that is just visible to the observer is given by: </P>

How far can you see from top of mount everest