Atmospheric refraction is a phenomenon in which the path of light or other electromagnetic waves is bent as they pass through the Earth’s atmosphere. This bending of light occurs because the speed of light varies with the density of the medium it is traveling through, and the atmosphere is composed of layers with varying density due to differences in temperature and pressure.
Key points about atmospheric refraction:
- Bending of Light: When light or electromagnetic waves enter the Earth’s atmosphere from a vacuum or another medium, they slow down and bend slightly due to the increased density of the air. This bending causes the direction of the waves to change, making objects appear slightly displaced from their actual positions.
- Causes of Variation: Atmospheric refraction is most pronounced near the Earth’s surface because the density of the air decreases with altitude. Factors such as temperature, pressure, and humidity also influence the degree of refraction.
- Sunrise and Sunset: One of the most noticeable effects of atmospheric refraction is the apparent change in the position of the Sun during sunrise and sunset. The Sun often appears slightly above the horizon when it is actually below it, which is why we can still see it before it has fully risen or after it has set.
- Atmospheric Lensing: The Earth’s atmosphere acts like a lens, focusing light to some extent. This effect can be observed in the distortion of objects seen through the atmosphere, especially when they are near the horizon.
- Astronomical Observations: Astronomers take atmospheric refraction into account when making celestial observations because it can affect the apparent positions of stars and planets, particularly when they are near the horizon.
- Mirages: Mirage phenomena, such as superior mirages (objects appearing elevated) and inferior mirages (objects appearing lowered), are also the result of atmospheric refraction. Superior mirages can create the illusion of distant objects being visible when they are beyond the Earth’s curvature.
- Visual Effects: Atmospheric refraction can lead to various visual effects, including the distortion of images, twinkling of stars (stellar scintillation), and the appearance of a “green flash” at the moment of sunset or sunrise.
In summary, atmospheric refraction is the bending of light as it passes through the Earth’s atmosphere due to variations in air density. This phenomenon has a range of effects on the appearance of celestial objects and can cause objects to appear slightly displaced from their actual positions, especially near the horizon.