Question

Hello Rabbi, I’ve had a chance to study a bit of the well-known dispute between Magen Avraham and the Vilna Gaon regarding the halakhic times of the day—whether they are measured from dawn until nightfall, or from sunrise until sunset. I wanted to ask whether you have an opinion on the matter after studying the topic from both a scientific and a halakhic perspective—which of the two views seems more plausible? Also, I saw that the Vilna Gaon, in Orach Chayim 459 s.v. “mil” (if I remember correctly), cites the view of the natural scientists, the astronomers, and tries to prove from them against the view of Terumat HaDeshen that the day begins at dawn, because there are astronomical difficulties with that position—see there. Do today’s astronomers also hold that view? I’d be glad to hear the Rabbi’s opinion on the subject. In any case, this has a practical implication for me regarding how long I can sleep in the morning with respect to the time for reciting the Shema.