How can Muslims be called to the dawn prayer (Fajr prayer) in areas where there is no dawn, and to the sunset prayer (Maghrib prayer), in areas where the sun does not set?

In regions of the Arctic there are times in summer when the sun never goes down ("midnight sun") and times in winter where the sun never rises ("polar nights"). When there is no dawn and no sunset, how do Muslims in the Arctic know when to pray? Why did Allah not give everyone specific prayer times, so that they do not have to pretend that they live somewhere else?