Yom Tov Sheni -

The Second Festival Day

For Jews living outside Israel, major Jewish holidays (except for Yom Kippur) are often observed for an additional day called yom tov sheni shel galuyot. The two days of Yom Tov are observed in the Diaspora because the Sanhedrin’s messengers could not reach distant communities in time to inform the people of the Rosh Chodesh sighting. Therefore there was some question as to which day was correct for the observance of various Jewish holidays. A second day was therefore added to each holiday so that the correct date would not be missed...