Atmospheric Refraction is the bending of light as it passes through the Earth's atmosphere. This happens because the atmosphere has different layers of varying optical densities, which change the speed and path of incoming light.
Because of early sunrise (2 minutes) and delayed sunset (2 minutes) caused by atmospheric refraction, the length of our day on Earth is actually 4 minutes longer than it would be if the Earth had no atmosphere!
The Earth's atmosphere is not uniform. The air near the ground is generally warmer and optically rarer (less dense). As you go higher up, the air becomes cooler and optically denser.
When starlight or sunlight enters the Earth's atmosphere, it travels from a rarer medium (space/vacuum) into increasingly denser layers of air. According to the laws of refraction, light traveling from a rarer to a denser medium bends towards the normal. This continuous bending of light through the atmosphere is called atmospheric refraction.
Stars twinkle because of atmospheric refraction.
Planets are much closer to Earth than stars. While a star appears as a single tiny point source of light, a planet appears as an extended source (a collection of many point sources).
Even though the light from individual points on the planet undergoes refraction and flickers, the overall average brightness from all the points combined remains constant, cancelling out the twinkling effect.
We can see the sun about 2 minutes before the actual sunrise and 2 minutes after the actual sunset.
Just like the sun, when light from a star near the horizon enters the atmosphere, it bends downward. When our eyes trace this light back in a straight line, the star appears to be at a higher position than its actual physical location.
Yes! A mirage is an optical illusion caused by atmospheric refraction. Hot sand heats the air just above it, making it optically rarer than the cooler air above. Light from the sky bends upwards as it hits this hot layer, creating an illusion of a puddle of water reflecting the sky.
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