Sod Ha’ibur is a website about the Hebrew Calendar

It is not Mysticism — not Kabbalah

It is about Halachic Insight & Applied Science

The actual date our Hebrew Calendar began is presented here.

ור"ש בן לקיש מקפד על הדא מילתא חשש להיא דא"ר לעזר דא"ר לעזר והיתה ידי על הנביאים החוזים שוא והקוסמים כזב בסוד עמי לא יהיו זה סוד העיבור.

And Rabbi Shimon ben Lakish became angry concerning this matter. He was troubled because of what Rabbi Eleazar said, for Rabbi Eleazar said: And my hand shall be against the prophets that see falsehood, and divine lies; they shall not be in the secret council of my people (Ezekiel 13:9). [They shall not be in the secret council of my people] — this refers to the “Secret of the Intercalation.” (Talmud Yerushalmi, Rosh HaShanah, 2:6.)

Lunar Calendars were the rule in the ancient world. Many if not most were Lunisolar, adjusting to the seasons.

In my book Sod Ha’ibur — Origin of the Hebrew Calendar — Conflict between Rabban Gamliel and Rabbi Yehoshua
I present my search for the answer to a simple question I had after Rosh HaShanah 2002. Why don’t we see the New Moon after sunset on the first night of Rosh Hashanah. Some major things I learned from this quest are presented here.