Rafi Sahib, in addition to what Dr. Shabbir has already pointed out, I submit the following. Quran has provided guidance for establishing the dawn and dusk scenarios to make it easy for believers to do certain acts. It talks about ascertaining the Dawn or Al-Fajr in 2:187. I just checked Dawn/dusk hours for Oslo, Norway, at http://www.gaisma.com/en/location/oslo.html. You may see that even those places have defined Dawn and Dusk.