Editing Hebrew calendar (section)

===Karaite calendar===
[[Karaite Judaism|Karaites]] use the lunar month and the solar year, but the Karaite calendar differs from the current Rabbinic calendar in a number of ways. The Karaite calendar is identical to the Rabbinic calendar used before the Sanhedrin changed the Rabbinic calendar from the lunar, observation based, calendar to the current, mathematically based, calendar used in Rabbinic Judaism today.

In the lunar Karaite calendar, the beginning of each month, the [[Rosh Chodesh]], can be calculated, but is confirmed by the observation in [[Israel]] of the first sightings of the new moon.<ref>{{cite web|url=http://www.karaite-korner.org/new_moon.shtml|title=Karaite Korner – New Moon and the Hebrew Month|website=www.karaite-korner.org}}</ref> This may result in an occasional variation of a maximum of one day, depending on the inability to observe the new moon. The day is usually "picked up" in the next month.

The addition of the leap month (Adar II) is determined by observing in Israel the ripening of barley at a specific stage (defined by Karaite tradition) (called [[aviv]]),<ref>{{cite web|url=http://www.karaite-korner.org/abib.shtml|title=Aviv Barley in the Biblical Calendar – Nehemia's Wall|date=24 February 2016}}</ref> rather than using the calculated and fixed calendar of [[rabbinic Judaism]]. Occasionally this results in Karaites being one month ahead of other Jews using the calculated rabbinic calendar. The "lost" month would be "picked up" in the next cycle when Karaites would observe a leap month while other Jews would not.

Furthermore, the seasonal drift of the rabbinic calendar is avoided, resulting in the years affected by the drift starting one month earlier in the Karaite calendar.

Also, the four rules of postponement of the rabbinic calendar are not applied, since they are not mentioned in the [[Tanakh]]. This can affect the dates observed for all the Jewish holidays in a particular year by one or two days.

In the Middle Ages many Karaite Jews outside Israel followed the calculated rabbinic calendar, because it was not possible to retrieve accurate aviv barley data from the land of Israel. However, since the establishment of the [[State of Israel]], and especially since the [[Six-Day War]], the Karaite Jews that have made ''[[aliyah]]'' can now again use the observational calendar.