The Effect Of Atmospheric Refraction On The Observed Elevation Angles Of Peaks Atmospheric refraction slightly increases the observed elevation angle of a peak relative to the observer. The effect is actually quite complicated, since it depends on the precise atmospheric conditions, including atmospheric pressure, temperature, and water vapor content, and thus varies with time and the altitudes of the observer and the observed peak.
Refraction is caused by two effects.
First, light likes to travel on the path that gets to the observer in the minimum time. The speed of light is the speed of light in a vacuum divided by the index of refraction. Second, the index of refraction of the atmosphere depends on atmospheric pressure and amount of water present, which change with height in the atmosphere. Therefore light actually travels on a curved path in the atmosphere from one object to another. The path goes higher than the straight-line distance in order to take advantage of the faster speed higher in the atmosphere.