my physics teacher told me about the refraction and its applications one of them was
2 minutes of early sunrise and after she explained this effect she concluded that days are
2 minutes longer than one would naively presume.

However, I think that her conclusion is wrong because
if sunrise is considered then sunset should also be considered and according to me sunsets should be 2 minutes late therefore the day time is increased by 4 minutes and not 2 minutes over the naive calculation.

According to me, the situation looks something like this:
enter image description here
Is this idea of mine correct or not? And if we both are wrong, then what should be the right conclusion and why ?

  • $\begingroup$ Your image, of course, should have the south pole in the centre. But that's hardly important. $\endgroup$ – Emilio Pisanty Feb 10 '14 at 15:12

Yes, you are correct. The sun is still/already below the horizon at the time of apparent sunrise/sunset, and each of these effects will extend the length of each day by exactly the same amount because the situation is completely symmetrical.

Well caught!

  • 2
    $\begingroup$ Strictly speaking, the situation is not exactly symmetrical: 1) the length of the day depends on the declination of the sun, which changes slightly between sunrise and sunset; 2) the refraction of the atmosphere depends on atmospheric conditions; 3) the earth is not an exact spheroid. But these effects are very small. $\endgroup$ – Pulsar Feb 9 '14 at 14:18

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