Advanced Sunrise And Delayed Sunset

Did you know that we actually see the sunrise about 2 minutes before the sun is actually at that perceived position and Did you know that the sunset that we see is actually of a sun that has, in reality, already set? So why these different perceptions? It is because of a phenomenon termed as refraction of light.

What is refraction of light? Simply put, a ray of light ‘bends’ when it travels from one medium to another. This ‘bending of light’ is called refraction of light. If the light ray travels from a rare medium to a denser medium, it bends towards the imaginary normal and if it travels from a dense medium to a rarer medium, it bends away from the imaginary normal. Depending on the density of the different medium, the speed of the travelling light ray keeps varying, and this causes it to slow down or speed up, therefore bending in the process.

Advanced Sunrise

Effect of refraction of light on sunrise and sunset

So how this refraction of light is connected to our advanced sunrise and delayed sunset? Imagine the journey of light rays from the sun. At first, the journey of light is through vacuum and then through the atmosphere of the earth and then it is finally seen by us. At first, vacuum will be act as a rarer medium and the earth’s atmosphere with all its temperature changes, winds, different gases, will be a denser medium in comparison to that.

During sunrise, the light rays bend due to our atmosphere and we see the sun early even though the sun is just below the horizon. Similarly, at sunset, due to the same bending of light rays, we see the apparent position of the sun, not the actual position.

To sum up, due to refraction we see the sun rise about two minutes before it’s actually there and during sunset we see it for around two minutes more, even though it has already moved from that position.

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Practise This Question

Why does sky appers blue ?