As defined in Wikipedia, refraction is:

The change in direction of a wave due to a change in its transmission medium.

In our case, the wave changing direction is the visible light, and the transmission medium is atmospheric air.

Air temperature varies along the height, decreasing from surface to tropopause, approximately at 11.000 meters above sea level.

This temperature change modifies air properties, specifically it changes density and so it changes its refractive index.

When looking at a distant mountain, the line of sight is not always at the same height above sea level, as shown in this figure:
This variation causes the travelling light to cross air at different conditions, curving its trajectory as a consequence of changing refractive index.

And then allowing hidden mountain to show up above the horizon.

This light curving effect of refraction can be clearly seen in this picture of the rising sun, with a deformed shape as a consequence:

Sunrise as seen from Vistabella del Maestrazgo (1.246 meters)

For more information:


5 thoughts on “Refraction

  1. So you guys actually think you are taking pictures of mirages?? Or do you just have to put the geometry and refraction material so it makes sense why you can actually do what you do?


  2. Also the sun isn’t a solid object like a mountain? How can you clearly see refraction on the sun when it’s a big ball of radiation? It would always have a deformed shape, no?


  3. Both those images showing how we see another mountain from the top of another mountain are wrong, and if you can’t see it you’re not using any critical thinking. All human beings stand vertical (FACT) and look out at a 90 degree angle across horizontally at the horizon (FACT). We DON’T look across at the strange angle (looks like 125 degrees) that is portrayed in those two images. That wikipedia article on refraction is more brainwashing against what we do, and see in reality with our eyes.


  4. @Jim Slim
    Good point it’s not 125, but let me explain how I would excuse the author;)
    It’s obviously exaggerated all in the picture, however I suppose it was only meant to illustrate the fact that when looking at very distant object the angle may become non-negligible. For example the angle between objects 200 km away from each other is 200 / 40000 * 360 = 2 degrees. Right, that’s just 2 degrees, but those 2 degrees, this little curve of earth is crucial. If 92 was illustrated instead of 125 nobody would notice that!


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