text: The heated sands warms up their overhead air, causing the reflection factor of it to be different from upper layers which is much colder. Therefore, the low-angle light rays (e.g. 10 to 20 degrees to horizon) may reflect horizontally or with a slight up-angle and reaches the eyes. Now, what our brain may imagine by this signal is a decisive image: human used to see the sky in the water, therefore if he/she sees these light rays then thinks that there is a water next to horizon which reflects back the sky light-rays.