When does a month begin in the Sacred Calendar? Does it begin on the day of the astronomical new moon (conjunction), or when the new moon is first sighted with the naked eye?

A month in the sacred calendar begins with a first sighting of the new moon. An 'astronomical new moon' (conjunction) occurs when the sun and moon are in a straight line with the center of the earth. The new moon is not visible to the naked eye at this time; but becomes visible between about 15 and 48 (or more) hours later. In ancient days months began when the new moon was first seen with the naked eye. The ancients literally 'looked out' for the new moon and when it was seen they pronounced the start of the new month. They didn't publish the calendar several months or years in advance as we do today; but started each month when they actually saw the new moon. That is the original and best way to determine the beginning of a month. It completely eliminates the one day discrepancies that even the most conscientiously produced pre-printed calendars are liable to contain.

When, however, astronomers began to calculate the circuit of the moon around the earth, conjunction times became available and calendars based on these times began to be produced, months or even years in advance. The question is: What should we do, now that conjunction times and phases of the moon charts have become available? Do we use computer produced calculations and print a calendar in advance or not? Our answer is as follows. Some Christian groups publish calendars in advance by using mathematical calculations of some sort. However, because the ancient method was to lookout for the new moon each month, we use computer calculations but also allow a certain period of time for the new moon to become visible, before determining the start of each month. This means that after we have made an allowance for a first sighting with the naked eye, the pre-printed calendar we publish is very much in line with the sacred calendar used in ancient Israel. In 1978 we asked a group of believers in Jerusalem to confirm our findings by actually checking the calendar we published against first sightings of the new crescent moon.

The next question is: How long after a conjunction does the new born crescent become visible? The answer is: It is not possible to infallibly predict the exact date and time of the first sighting of a new moon. Various factors such as atmospheric pressure, temperature, humidity along the light path, altitude, latitude/longitude, fog, cloud/dust cover, glare etc. can all affect a first sighting. That is the reason why in the calendar and festival charts we publish we use the words: "a likely first sighting should occur," because no one can infallibly predict the moment when the new moon will become visible to the naked eye. The general consensus of authoritative opinion is that a first sighting of the new moon could occur any time between about 15 and 48 hours after a conjunction.

Note: The reader should remember that pre-printed calendars based on calculations were not used by the ancient Israelites. They literally looked out for the new moon each month and then counted to the Feasts. This is still the best method.