Snell’s Law explains the bending of light (refraction) as it moves between two media with different refractive indices. In the atmosphere, this principle helps explain how light bends when passing through layers of air with varying densities and temperatures.
Atmospheric Refraction and Snell’s Law:
- Air as a layered medium:
The atmosphere isn’t uniform; its density and temperature change with height. Cooler, denser air near the ground has a higher refractive index, while warmer, less dense air higher up has a lower refractive index. - Gradual bending:
As light travels from a cooler to a warmer layer (or vice versa), it passes through layers with slightly different refractive indices. According to Snell’s Law, when light enters a medium with a lower refractive index, it bends away from the normal; when it enters a medium with a higher refractive index, it bends toward the normal. - Curved path:
Because the change is gradual, the light doesn’t bend at a single sharp boundary but instead follows a smooth, curved path. This causes objects like the sun or stars to appear slightly shifted from their true positions, especially near the horizon. - Mirages:
In extreme cases, such as over hot roads, light bends so much that it creates the illusion of water. This happens when Snell’s Law is applied continuously across layers, and the bending becomes strong enough to turn into total internal reflection.
So, Snell’s Law explains how and why light bends through the atmosphere, leading to optical illusions and shifts in apparent position of celestial and terrestrial objects.