12 months

1 Chronicles 27:15 - The twelfth, for the twelfth month, was Heldai the Netophathite, from the family of Othniel. There were 24,000 men in his division.

I have wondered for some time how many months were in the ancient Hebrew calendar. I've read this text several times, but I must not have been thinking about this topic at the same time until now.

Here we see (in context) that there were 12 months in their year. If they counted months according to phases of the moon, then their year (at least at David's time) was shorter than ours today by quite a few days.

If there are 28 days from new moon to new moon (or full moon to full moon), then their year was 28 x 12 = 336 days. That's 29 days, or a full month, short of our current year. Did they not count their months this way?

If they had had 13 months in a year, it would have worked out much better. I wonder if the length of time it takes for either the moon to orbit the earth or for the earth to orbit the sun (or both) has changed enough over the millenia to make up for this difference.