Yom Kippur for Two Days

I was wondering why Yom Kippur is not observed for two days as the other major holidays in the Diaspora. I know it would be almost impossible, but if there is a doubt when Rosh Hashanah is (and so we keep it for two days), why shouldn’t there be the same doubt about Yom Kippur?

The Aish Rabbi Replies:

Thank you for raising the good issue. The reason is because we do not really have a doubt as to when Yom Kippur or any of the other holidays fall out today. Unlike in the days of the Mishna, when the months were set based on eyewitness sightings of the new moon, today we follow a set calendar. As a result, we know the precise dates of all the holidays every year, going forward indefinitely.

If so, why do Jews in the Diaspora still observe the other major holidays for two days? The Talmud explains “the custom of their forefathers is in their hands” (Beitzah 4b). Today, two days of yom tov are not observed out of doubt but because of an accepted custom. (This is why a person who lives outside of Israel keeps two days even if he is visiting Israel for a holiday. He keeps two days not because he doesn’t know the dates of yom tov, but because we must observe our local customs even if we are away from home.)

Yom Kippur, however, is different in that a custom was never accepted to observe it for two days. It would have been much too difficult and dangerous for most people, and so it never became the practice. Thus, today when we have no actual doubt of the date of Yom Kippur, there is no reason to observe it for two days.

It’s interesting to note that in the days of the Talmud – when there really was a doubt about the calendar – there were rabbis who fasted two days (see Talmud Rosh Hashanah 21a). But thankfully, that never became the accepted custom.

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