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Question
Explain why, the sun can be seen about two minutes before actual sunrise. Draw a diagram to Illustrate your answer.
Solution
Sunrise takes place when the sun is just above the horizon, but the atmospheric refraction of light makes the sun appear two minutes before sunrise. When the sun is slightly below the horizon, the sun's rays travel from the vacuum of space to the denser air of the earth's atmosphere. When sunlight passes from a rarer medium, namely, vacuum, to the denser medium of the air in the earth's atmosphere, it bends or refracts downwards. Owing to this refraction, the sun appears to be raised above the horizon even though it is slightly below the horizon.
In the figure below, the actual position of the sun is just below the horizon, but it appears to be just above the horizon, owing to atmospheric refraction. As a result, the sun appears to rise two minutes before the actual sunrise.
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