I listened to a shiur on Shavuos by R' Fuerst on my ride to work this mornig. It was one of those shiurim that R' Fuerst himself introduced by saying, "This is going to be a really interesting shiur!" There was palpable excitement in his delivery; he sounded like a kid in a candy shop. It was one of those things where you start with a seemingly trivial question and it blows up into a titanic of fundamental questions. The start was, "Since you know Shavous has to be on 6th of Sivan and that Shavous is 50 days after Pesach, then once you know rosh chodesh Nissan, you know exactly when both rosh chodesh Iyar and rosh chodesh Sivan; so why do you need testimony for those two months? In the course of answering that question, we discovered that it is not so obvious that Shavous has to be on the 6th, nor even that Shavous and Matan Torah have to coincide. I think you should listen to the shiur, if for no reason other than to hear R' Fuerst sounding like a kid with a new toy.
Along the way, we were introduced to several ways to understand both why there are two days of Shavuos outside of Eretz Yisrael. One answer depends on a fundamental difference between Jews and goyim that is noted by the Hafla'ah: our 24 day is a night followed by a day; their 24 day is a day followed by a night. So what, you ask. So this: We know that the Avos kept all the mitzvos and we also that they were not Jews -- after all, the Torah had not yet been given/accepted. One of the mitzvos, of course, is Shabbos. Shabbos is so important that it is a capital crime for a Jew violate it. However, it is also a sign/covenant between HaShem and his treasured nation, so it is a capital crime for a non-Jew to keep Shabbos! A bit of a quandary, no?
One of the answers given to how the Avos dealt with this dilemma was to wear tzitzis: Jews are obligated to wear them so they have the status of clothing; non-Jews are not required to wear them, so they are just carrying strings. I have not been comfortable with that answer for quite some time. First, that means the Avos would have had to make a point of walking in a r'shus ha'rabim d'oraisa every Shabbos. That's not as easy as you might think, especially since the Avos did not always live in metropolitan areas with 600,000 people milling about each day. Worse, though, even if a Jew wears tzitzis that are only safeik kosher, there's no issur d'oraisa to wear them on Shabbos. If the Avos were wearing them because of a safeik in their status (vis a vis Jew/goy), then it's very likely there is no issur at all to wear them even in a r'shus ha'rabim d'oraisa.
With the yesod of the Hafla'ah, though, there is a very simple answer. Shabbos for a goy begins Saturday morning and ends Sunday morning. As long as Avraham Avinu made havdalah on Saturday night, he had covered his bases. Even better, there is not even a question of "malacha sh'ein tzricha l'gufa" -- one making havdala really wants to make a fire in order to have a fire. Isn't that just way too cool for words!?
In case you think I am over-excited about this; here's the deal: I was never told to violate Shabbos when I was going through my geirus process. (Maybe I did out of sheer ignorance, but again; that's eino miskaven and only assur m'd'rabanan.) As I learned more, I realized how bad that was... violating a capital crime every week is not something I want on my record. But I did make havdala every week once I started my conversion process in earnest, so I am covered!
Whew... I know it's only one thing off my plate, but every little bit helps.