The Mishna (Berakhot 4:1) brings the opinion of R' Yehuda to the effect that the latest time for shacharit is the fourth hour of the day. In explaining R' Yehuda's opinion, Kehati elaborates upon the nature of halakhic hours (being equal divisions of the day-time, rather than fixed units of time) and brings an example that commences as follows:
למשל אם נקח יום מימי תמוז הארוכים, וכגון שעלה בו השחר ב-2 לפי שעוננו וזמן צאת הכוכבים היה ב-8, דהיינו שארכו של יום זה 18 שעות, נמצאת השעה הזמנית של אותו יום שעה ומחצה לפי שעוננו
My paraphrastic translation:
By way of an example, if we were to take a day from the month of Tammuz (in which the days are longer), in which the sun comes up at 2:00 by our watches and the stars come out at 8:00pm, then the length of such a day would be 18 hours and an halakhic hour would be found to be 1.5 hours in length (by our reckoning).
I have no problem with the calculation. What I do have a problem with is the assertion that the sun ever, anywhere, comes up at 2:00 in the morning. In fact, having spent no small amount of time at myzmanim.com, I cannot even find a habitable corner of the globe on which the sun ever comes up much earlier than 4:00am.
Is the halakhic definition of dawn such that it could ever be two hours (or more) before the first rays of sunshine?