The ancient method of certifying the new moon in the Land of Israel in ancient times is described in Mishnah Rosh Hashanah 2:6. Witnesses would come to Jerusalem and testify before the Sanhedrin that they had seen the new moon. They would be asked: "Say how you saw the moon.

  • [Was it] in front of the sun or behind the sun?
  • To its north or to its south?
  • How high was [the moon over the horizon]?
  • In which direction did it tilt?
  • And how wide was it?"

And later in 2:8 we have this:

Rabban Gamliel had a diagram of the different forms of the moon drawn on a tablet that hung on the wall of his attic, which he would show to the laymen who came to testify about the new moon but were unable to describe adequately what they had seen. And he would say to them: Did you see a form like this or like this?

Nearby passages mention the day when the new moon was "expected", but testimony was still needed to confirm the expectation, and testimony would apparently be accepted that contradicted the expectation, within the constraints that each month could only be either 29 ('deficient') or 30 days ('full'), and each year of 12 months had to total 354 days.

This method would allow the testimony of untrained witnesses to be evaluated and either accepted or rejected. And perhaps there were additional 'standard questions' beyond what is written here.

How would the answers to these questions from witnesses allow a competent ancient astronomer who understands the moon's motion in the heavens to decide:

  • whether the testimony is both accurate and truthful (ie to detect impossible answers)?
  • whether the new moon had in fact occurred before or after apparent sunset or sunrise on a given day (at the place of observation)?

We should assume that the questioner has not already reached a conclusion (say the sky was cloudy in Jerusalem or wherever the questioner was) and must rely on the witness testimony to decide the new moon.

The Mishnah passage itself explains that if the witness says the moon was "in front" of the sun--rising or setting before the sun I suppose--his testimony can be discounted as this is clearly impossible after a new moon. However, the new moon does set first sometimes; perhaps this is why north or south was asked. But I'm not clear about the other questions. How do they inform the questioner of today's concepts of right-ascension, declination, etc? Is this level of detail even useful for the purpose, beyond for detecting erroneous testimony?

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    $\begingroup$ How is this question deficient to deserve a downvote? $\endgroup$
    – wberry
    Commented Apr 12 at 13:56
  • $\begingroup$ I think your question is fine. I think it's a challenge to answer, but I don't see any problems with it, so I'll add a bounty. $\endgroup$
    – uhoh
    Commented Apr 25 at 22:52
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    $\begingroup$ The Moon's orbit is nearly circular, so computing its position over short periods of time is rather trivial. An observation of the Moon within a few days of the new Moon likely would have been far more that sufficient. $\endgroup$ Commented Apr 27 at 4:32
  • $\begingroup$ It is likely possible for the new moon to rise after the Sun. Eg as an extreme example, if the moon if on the South side of the Sun, and the observer near the North pole, the Sun may rise, but the moon might not rise at all that day. The options get slimmer closer to the equator though. $\endgroup$ Commented Apr 29 at 15:46
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    $\begingroup$ @uhoh Thanks for offering a bounty. I didn't want it to simply expire without trying my hand with what I have been able to deduce on my own. $\endgroup$
    – wberry
    Commented May 1 at 0:08

1 Answer 1


The questions posed to the witnesses can be used for three purposes:

  • To evaluate whether an individual witness' testimony is plausible or not.
  • To decide between two or more witnesses, or groups of witnesses, who provide conflicting testimony. Witnesses who saw the new moon on different days may report different details but both deemed trustworthy.
  • In the probably rare case where the moon could not be observed anywhere in the Land of Israel at the first sunset due to cloud cover, the accepted witness testimony could be used to decide whether the new moon had actually occurred one or more days before the witnesses observed it.

Implied Questions

While not explicitly listed among the questions, it is implied that each witness will be additionally asked:

  • When exactly did you see the new moon?
  • Where exactly were you when you saw it?

Assumption of Latitude

Culturally, this process was anchored in the middle east, especially in Jerusalem but the 'seat of Moses' was in Babylon and then Persia during the captivity as well. Also, witnesses could come to the elders from up to a day's horse ride away. Therefore, terrestrial latitude between 30 and 35 degrees north should be assumed. (Therefore, phenomena that occur only outside those latitudes, like the sun never rising or setting for many days north of the arctic circle, can be neglected.)

Indicators Gauged From Each Question

  • When did you see the new moon? Surely each witness would be asked this. The witness' answer should be used as a baseline to evaluate the plausibility of the other answers. If multiple witnesses or groups of witnesses testify to different days for the new moon, the other answers will help to decide between them. If a witness claims to have seen the new moon in the morning, the testimony can be doubted, as sunrise will make it very difficult to observe the crescent moon that follows it. A witness who additionally claims that the new moon preceded the sun in rising has not actually seen the new moon.
  • Where were you when you saw the new moon? Surely each witness would be asked this as well. A witness who claims to have seen the new moon from Ein Gedi just as the first evening stars were appearing can be discounted, as the terrain would make such observation impossible. A witness who saw the new moon from the Mediterranean coast, or a city on a hill with no terrain obstacles, might be considered more reliable than one who saw the new moon through palm trees in the plain.
  • Was it in front of the sun or behind the sun? The purpose of this question is explained in the Mishnah passage itself. If the witness says the new moon was in front of the sun, this is to be considered impossible and the testimony distrusted. While it is possible for the new moon to set before the sun, it would be extremely difficult to actually observe this at the terrestrial latitude of Jerusalem with the naked eye.
  • To its north or to its south? Meaning, was the new moon on the north or south side of the sun's path through the sky (the ecliptic)? This answer in combination with the reported 'tilt' (orientation) of the crescent can be used to detect impossible answers. If the moon is to the south of the sun, its crescent must tilt towards the north side. Also, a skilled ancient astrologer would be well aware of the current lunar path through the sky relative to the ecliptic, and easily identify a wrong reply to this question. This level of knowledge is inferred from the existence of the question, and also from the Saros cycle which was known to the Babylonians since before the captivity.
  • How high was it? Meaning, how high above the horizon was the new moon? The witness might gesture towards the location in the sky where the new moon was seen. This could be compared to the current height of the moon over horizon at sunset, and implausible testimony discounted. Potentially, the answer could indicate that the new moon had actually occurred the day before it was first observed. But the Mishnah section discusses the importance of encouraging people to come to Jerusalem to testify to the new moon, and not to have them leave disappointed. So it should be assumed that at least a few witnesses would normally have been able to observe the new moon immediately from somewhere in the Land of Israel, even during the rainy season.
  • In which direction did it tilt? Most likely this meant to ask about the orientation of the crescent. The crescent of the new moon should 'tilt towards the sun', ie an imaginary line drawn from the moon's center outward through the center of the arc of the crescent should pass through the center point of the sun. If the witness testimony differs from this, the testimony can be discounted. Having a pictorial table for witnesses to choose from, such as the one described in the Mishnah, would be quite helpful here.
  • And how wide was it? Most likely this meant to ask about the apparent phase of the moon. Given testimony on the observed phase and height over the horizon, a skilled ancient astronomer should be able to identify if the answers are implausible in combination, or in comparison to the current appearance of the moon after sunset. A new moon that has occurred very recently will appear very low in the sky after sunset, and with a sliver of a crescent; whereas one that occurred during the previous night would be somewhat higher in the sky with a thicker crescent. Having a pictorial table for witnesses to choose from, such as the one described in the Mishnah, would be quite helpful here as well.

And so we see that witness testimony on these seven questions, two of them assumed, actually provide a quite complete account of the new moon. These details could be checked either against each other, against conflicting testimony from other witnesses, or against subsequent observations of the moon in order to discount confused or fabricated testimony. They also allowed a skilled astrologer (astronomy was not considered a separate discipline back then) to determine in cases of cloud cover whether the new moon had in fact occurred earlier than when it was first observed.


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