1. Definition: Atmospheric refraction is the bending of light as it passes through the Earth’s atmosphere. This bending is caused by variations in the refractive index of air, which is influenced by factors like temperature, pressure, and humidity.
2. Causes of Refraction: Atmospheric refraction occurs because the speed of light changes when it travels through different mediums. As light enters Earth’s atmosphere from space, it slows down and bends due to differences in air density at different altitudes.
3. Apparent Position: Due to atmospheric refraction, celestial objects like the Sun, Moon, and stars appear slightly higher in the sky than they actually are when they are near the horizon. This is why the Sun can still be visible even after it has technically set.
4. Twinkling of Stars: The twinkling of stars is caused by the constant variation in the refractive index of the atmosphere. As starlight passes through different layers of the atmosphere, it undergoes random refractions, causing the star’s brightness to appear to flicker.
5. Green Flash: Atmospheric refraction can also create optical phenomena such as the green flash. This occurs when the Sun briefly flashes green just before sunset or after sunrise due to the dispersion of light as it passes through the atmosphere.
6. Sunrise and Sunset: The Sun appears flattened when it is near the horizon during sunrise and sunset. This is because the bottom part of the Sun’s disk is refracted more than the top part, creating an apparent distortion.
7. Mirages: Mirages, like the “desert mirage” or “water mirage,” are also a result of atmospheric refraction. Hot air near the ground bends light rays, creating the illusion of water or objects that are not really there.
8. Temperature Gradient: The degree of atmospheric refraction depends on the temperature gradient in the atmosphere. A steep temperature gradient can result in more pronounced bending of light.
9. Astronomical Observations: Astronomers must take into account atmospheric refraction when making precise observations of celestial objects, especially when objects are close to the horizon.
10. Navigation: Atmospheric refraction can affect navigation, especially in aviation and marine activities, as it can cause objects to appear in slightly different positions than they actually are.

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