This is the third of six articles in which we’re discussing different aspects of the Hebrew calendar. If you’ve not read part 1 yet, please do so as it will explain the importance of this topic and it defines the terms evening and morning. In part 2 we concluded that the correct reckoning of a day is that it starts in the morning, not the evening, and that the current Jewish custom of starting the day in the evening is not Biblical but Babylonian.

The Bible does not explicitly tell us when a month begins. Jewish tradition claims that the month begins with the first sighting of the crescent moon, but it should come as no surprise to learn that this too was a Babylonian practice with no scriptural mandate. It goes hand-in-hand with the Babylonian day beginning in the evening, as the first crescent of the new moon can first be seen near the horizon shortly after sunset.

The small amount of Biblical evidence we have is that the month began with the new moon, not afterwards with the first sighting of the crescent moon.

This command is repeated slightly differently in the Psalms:

Harmonising these two passages we can see that the beginning of the months must be either on the new moon, the full moon, or the solemn feast day. The solemn feast day is the Feast of Passover, which can be seen from Exodus 12:42. But Numbers 10:10 shows that it is not just the Feast of Passover but all the appointed feasts. As neither Passover, nor most of the other appointed feasts begin at the start of the month (the Feast of Trumpets in the seventh month being the only exception) by inference the new month must begin on either the new or the full moon. The book of 2 Chronicles helps narrow this down even further:

Here the new moons are shown as being separate from the three appointed feasts. Two of those feasts—the Feast of Unleavened Bread and the Feast of Tabernacles—begin on the 15th day of the month, which is at the exact opposite phase of the moon from the beginning of the month. If the month began at the full moon, those feasts would be at the new moon, and the passage in 2 Chronicles wouldn’t make sense. But if the month began at the new moon, then those feasts would begin at the full moon, and the inclusion of the new moon in that verse would make sense.

Another passage that associates the new moon with the first day of the month is found in the book of 1 Samuel:

Not only does this passage show us that the new month began with the new moon, it also shows us that the new month began “when the new moon has come”, not necessarily when the first crescent of the new moon was seen, as Jewish tradition holds. This is made clear a few verses earlier.

If the month was dependent on the sighting of the crescent moon then the month would usually begin a day or two after the new moon; yet the passage in 1 Samuel 20 shows that it began with the new moon. Furthermore, it would not be possible to know in advance whether the crescent moon would be able to be seen on the first day following the new moon, which means the month could have begun either the following day or the day after, yet such uncertainty is not present in the verse in 1 Samuel.

Requiring a visual sighting would also place the full moon on the 13th or 14th of the month, whereas the Feast of Unleavened Bread and Feast of Tabernacles begin on the 15th, which would be a day or two after the full moon. On the other hand, a new month that begins with the new moon (and not with the sighting of the crescent moon a day or two later) would see those feasts falling right on the full moon, which is more consistent with those feasts being the “appointed times” of God, which, as we discussed in part 1 of this series, are governed by the movements of the sun and the moon.

The little the Bible does reveal on this topic shows that it is the new moon—that is, the moment of conjunction between the moon and the sun when the moon is invisible—not the first sighting of the crescent moon, that determines the beginning of a month. The day that dawns on or after the moment of conjunction will begin the new month.

In part 4 we will attempt to answer the question of when a year should begin.