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. $\endgroup$ Feb 10, 2014 at 15:12

1 Answer 1


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, 2014 at 14:18

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.