By: Rabbi Ari Enkin
No, no, this post will not address nor debate whether visitors to Israel should observe one day of Yom Tov or two. There’s more than enough literature on that already.
Instead, this post will focus on a very unique aspect of the issue which seems to have gone completely unnoticed.
The source for the debate regarding whether visitors to Israel should observe one day of Yom Tov or two originates in the Mishna. There we learn that one who travels to a new place must observe all the restrictions which are practiced in the place from which one left, as well as the restrictions which are practiced in the place one now finds oneself. Of course, as the Gemara explains, this is true only if one intends to return to the place from which one came. If one intends to remain in the new location permanently, one immediately assumes resident status in the new place and one only observes the restrictions that are practiced there.
Those who rule that visitors to Israel must observe two days of Yom Tov cite this Mishna as their source, arguing that just as a second day of Yom Tov is observed in the place from which one came, so too, it must be observed in the place in which one now finds oneself (i.e. Israel), as well.
The Chacham Tzvi is the leading figure who advocates that visitors to Israel should only observe one day of Yom Tov. He argues that the Mishna’s requirement for one to observe the restrictions of the place one has left is simply not relevant with regards to Yom Tov. He explains that the issue of a second day of Yom Tov is unlike any other custom that the Mishna refers to, because it is something which is inherently subject to a geographical location â€“ the Diaspora.Â
To further explain, when the Mishna rules that visitors must observe all of the restrictions normally observed in their home town in their new location, it only refers to customs which are or can be practiced in the new location by the residents of that place. The Mishna’s example of one such custom is that of not performing any work on Erev Pesach. Although in truth there are very few communities which observe this custom today, it is, however, a custom which can theoretically be observed in any community equally, whether in Israel or in the Diaspora. Yom Tov Sheini, however, is something which simply cannot be observed or adopted by the residents of Eretz Yisrael. Therefore, it is not something which was never subject to the ruling of the Mishna.
In other words, what the Chacham Tzvi is essentially saying is that just as there are “mitzvot hateluyot ba’aretz“, mitzvot which are subject to the Land of Israel, there also “mitzvot hateluyot b’chutz la’aretz” mitzvot which are subject to the Diaspora.
 To cut to the chase on that issue: If you ask a Chareidi affiliated rabbi, you will be told to keep 2 days of Yom Tov. If you ask a YU [and similar streams] affiliated rabbi, you are likely to be told to keep “a day and a half”, and if you ask a Mizrachi/Bnei Akiva affiliated rabbi, Chabad, and many Sefardi rabbis, you are likely to be told to keep one day. Ask your rabbi what’s right for you.  Pesachim 50a  Chacham Tzvi 167. See also: Shulchan Aruch Harav, OC 496:11. Also of interest: “In recent years, this opinion of the Chacham Tzvi has gained more popularity among the poskim” â€“Rabbi Herschel Schachter, cited at: http://www.torahweb.org/torah/special/2003/rsch_ytsheini.html