Rosh Chodesh - How to Spot a New Moon
- Gene Keener
- Apr 2
- 2 min read
Updated: Apr 8

Rosh Chodesh - How to Spot a New Moon
Originally, the New Moon was not fixed by astronomical calculations but was solemnly proclaimed after witnesses had testified to the reappearance of the crescent of the moon.
Encyclopaedia Judaica Pg 150 Vol 15. Ed. Michael Berenbaum and Fred Skolnik. Vol. 15. 2nd ed. Detroit: Macmillan Reference USA, 2007. p150-151. COPYRIGHT 2007 Keter Publishing House Ltd. Aaron Rothkoff and Jody Myers
Philo was a prominent Jewish leader who lived in Alexandria from about 20 B.C.E. to about 50 C.E. and was a contemporary of both [Yeshua] the Messiah and Paul. He was aware of what the Savior and His followers considered was the new moon. In his Treatise on the Special Laws, Book II, XI (41), Philo discusses the Biblical observances. Note how he describes the new moon:
“[It] is that which comes after the conjunction, which… [is] the day of the new moon in each month.” In his detailed discussion of the new moon, Philo describes what constitutes a new moon: “…at the time of the new moon, the sun begins to illuminate the moon with a light which is visible to the outward senses, and then she displays her own beauty to the beholders.”
As Philo noted, the new moon follows the conjunction but it is not the conjunction itself. His observation reveals to us what was considered the new moon in [Yeshua’s] day and what the Savior Himself also observed as the new moon. This should be all we need to know to realize what still constitutes the Biblical new moon today.
Treatise on the Special Laws, Book II, XI (41), Philo, additional commentary follows:
THE THIRD FESTIVAL
XXVI. (140) Following the order which we have adopted, we proceed to speak of the third festival, that of the new moon. First of all, because it is the beginning of the month, and the beginning, whether of number or of time, is honourable. Secondly, because at this time there is nothing in the whole of heaven destitute of light. (141) Thirdly, because at that period the more powerful and important body gives a portion of necessary assistance to the less important and weaker body; for, at the time of the new moon, the sun begins to illuminate the moon with a light which is visible to the outward senses, and then she displays her own beauty to the beholders.
[excerpt from pdf]
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