[Avodah] Dawn's Early Light

[kennethgmiller at juno.com]

My shul subscribes (via webcast) to the Motzaei Shabbos Navi Shiur given each week by Rabbi Yisroel Reisman. He raised an interesting question this week, but I missed the answer (or perhaps he left it unanswered). Those who would like to hear the shiur can go to http://preview.tinyurl.com/2jvhzq (There is a fee.)

The title of the shiur (which I've taken for this thread) was "Dawn's Early Light", in which he goes into various aspects of the period of time from Alos Hashachar to Sunrise, and the period from Sunset to Tzeis Hakochavim. He noted that the Gemara (Pesachim 93-94) has various discussions about how long these intervals last, but there is one constant throughout that whole sugya: It is taken for granted that however long they last, they both last for the same duration.

The unanswered question is: But that makes no sense! It is much darker at Alos Hashachar (when the entire sky is pitch black except for a tiny bit of light on the eastern horizon) and not quite so dark at Tzeis Hakochavim (when only three medium-sized stars are visible scattered across the whole sky). Using these definitions, The time from Alos to Sunrise ought to be a lot longer than the time from Sunset to Tzeis.

Rabbi Reisman did note that in many communities (including mine) the time from Alos to Sunrise is taken to be 72 minutes year-round, while the time from Sunset to Tzeis is noticeably shorter. This difference fits our understanding of how the times are defined. But this distinction seems to have eluded everyone mentioned there in Pesachim. Does anyone comment on this oddity?

Akiva Miller