Extra holy day(s) observed by Jews living in the Diaspora on the festivals of Passover, Shavu'Ot, and Sukkot. They stem from a recurrent problem of Second Temple times--- fixing the correct date for each New Moon (and hence for any festival or fast that would occur during the month ahead) in the Jewish Calendar. Originally, visual observation of the New Moon was ascertained from reliable witnesses by the Sanhedrin in Jerusalem; once acceptable testimony had been obtained, a chain of beacons relayed the information to other communities and, at a later stage, messengers were dispatched to provide Jews living outside Erets Israel with the relevant information. There is reason to believe that this system of communication broke down as a result of the anarchy prevailing during the last days of the Temple. In order to make doubly sure that they would not observe a festival on the wrong date, Jews in the Diaspora began keeping two holy days (instead of one) at the beginning and the end of both Passover and Sukkot, and two also on Shavu'ot. Once a fixed calendar had been introduced in the fourth century CE, however, the date of each New Moon and festival was known in advance. Jews living in Babylonia therefore addressed an inquiry to the sages in Erets Israel, asking if it would not be logical to dispense with these "second festive days" (yom tov sheni shel galuyyot). The reply was that a custom hallowed by centuries of usage should still be maintained, even if the reason for its observance no longer applied.
Current practice throughout the Diaspora is to convert the first intermediate day of Passover and Sukkot into a second holy day (yom tov) and for Isru ḥag (the day after each festival's termination) to become the eighth day of Passover or the ninth day of Sukkot (Simḥat Torah being attached to Shemini Atseret). A second Seder is also held on Passover. Isru Ḥag likewise becomes the second day of Shavu'ot. Rosh Ha-Shanah is the only festival when even in the Land of Israel a second day is added to the biblical one-day festival. This was probably due to the fact that since the New Year falls right at the beginning of the month, even Jews in the Holy Land could have remained in a state of uncertainty if the announcement of the new month (Tishri) did not reach them in time. Nevertheless, there is ample reason to believe that the original practice in Erets Israel was to observe Rosh ha-Shanah for one day only, in accordance with the biblical description, and that the institution of the "second day" was a later innovation. The Day of Atonement, however, remains a one-day solemnity in the Diaspora as well as in Israel, because an extension of the fast would prove unduly severe.
Talmudic evidence (TJ, Er. 3:9) indicates that observance of these "second festive days" was considered a religious penalty for choosing to live in exile (Galut). Reform Jews do not observe the second day of festivals. The Conservative movement allows its rabbis and congregations freedom of choice in the matter, but the vast majority of Conservative congregations do observe the "second day." Israelis visiting abroad have a religious obligation to conform in public with the Diaspora practice; a Jew coming to Israel from overseas has to observe the second day of festivals unless he envisages aliyah at some point in the future.
