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Calculating the Calendar

While knowing which day is Rosh Hodesh [the beginning of the month] is needed usually just for the special prayers recited on that day, knowing the exact date of Rosh Hodesh from the day it is sighted is a matter of great importance when it will directly affect the observance of a Mo`ed (appointed time, i.e. a holiday). Truly, the most important observance for the calendar is that of the Aviv. For all other times, it is sufficient to know when Rosh Hodesh in fact occurred in order to determine when a given month has begun or ended.  Generally, what is known as the possibility of sighting (the calculation of when the moon will be able to be observed) is reliable. When it will not be reliable can also be calculated, and in those circumstances it is necessary to rely on observation. This said, it must be remembered that despite calculation we always rely on the actual sighting of the moon to determine the beginning and ending of the months regardless of whether we were able to calculate its appearance or not. There are several sites that report the sighting of the new moon. Amongst others, those who keep the Torah calendar can utilize the following Jewish and Muslim sites when attempting to determine when the new moon was sighted in Israel (referring to the Biblical boundaries of Israel). Keep in mind, they only list the actual sightings some time afterward and may not be up to date until later in the month:

http://www.geocities.com/royh_il/ (The Israel New Moon Society)

http://moonsighting.com/

http://www.icoproject.org/default.aspx (Islamic Crescent Observation Project)

Another thing to be careful with when reading the information on the latter site is that some Muslims believe that as soon as the moon is visible anywhere in the world they start the new month - even if it is not locally visible, i.e., if someone in the South Pacific sees the moon they start the new month even if the moon won't be visible in the Middle East until the next day. Others don't accept that. The sighting centres for this new moon site are based in Jerusalem and an area of Jordan that is within the boundaries of Biblical Israel. Therefore, if the moon is sighted there, it is good. If the moon is not sighted there, this does not mean it was not sighted elsewhere in Israel. Other sources must be checked in order to confirm this.

Prospective dates for the Mo`adim of the new year...

The projected dates for the Rashei Hodashim [first days of the months] and the Mo`adim [set/appointed times] are as follows (obviously all these projected dates require confirmation of the actual sighting of the new moons):

Projected Dates for Rashei Hodashim and Mo`adim
March 2012 - October 2012