Why there is flattening of sun at sunrise and sunset?
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It is due to the refraction of sunlight as it travels through Earth's atmosphere.
Sunlight enters the Earth's atmosphere from the vacuum of space. The refractive index of air with respect to vacuum is 1.0029. This means that the speed of light in air is 1.0029 times slower than the speed of light in vacuum. This causes the light rays to bend towards the normal (refraction).
During sunrise and sunset, light rays have to travel a longer distance through the atmosphere than in the afternoon, when the sun is directly overhead. The atmosphere isn't uniform and has a layered structure; this is because as altitude increases, air becomes thinner. Thus, the light rays are continuously refracted till they reach our eye. Refraction of light by these layers can make the sun appear flattened or distorted.
Objects closer to the horizon are raised upwards most and the lower limb of the Sun is raised more than the top making it appear oval.
Strangely enough, the sun is visible a little before (around 2 minutes) it actually crosses the horizon i.e the day appears to be 4 minutes longer than it actually is. This too, is due to refraction of sunlight!
Hope this helps!
Sunlight enters the Earth's atmosphere from the vacuum of space. The refractive index of air with respect to vacuum is 1.0029. This means that the speed of light in air is 1.0029 times slower than the speed of light in vacuum. This causes the light rays to bend towards the normal (refraction).
During sunrise and sunset, light rays have to travel a longer distance through the atmosphere than in the afternoon, when the sun is directly overhead. The atmosphere isn't uniform and has a layered structure; this is because as altitude increases, air becomes thinner. Thus, the light rays are continuously refracted till they reach our eye. Refraction of light by these layers can make the sun appear flattened or distorted.
Objects closer to the horizon are raised upwards most and the lower limb of the Sun is raised more than the top making it appear oval.
Strangely enough, the sun is visible a little before (around 2 minutes) it actually crosses the horizon i.e the day appears to be 4 minutes longer than it actually is. This too, is due to refraction of sunlight!
Hope this helps!
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