by Roy E. Hoffman and Tuvia Kaatz
for predicting the visibility of the Moon
ü Tables of Moon sightings updated each month a few days after the New Moon
The commandment (mitzvah) of sanctifying the month is the first one which the Children of Israel were commanded on leaving Egypt. This commandment is of great importance because the dates of the festivals, including over 60 commandments, depend on it. In addition to sanctifying months according to the appearance of the New Moon, the Hebrew calendar depends on leap years (extended by an extra month) that depend on the position of the Sun, ripeness of grains, etc.
For over a thousand years, the Hebrew calendar has been fixed by calculation. Today, the Hebrew calendar does not match that fixed by observing the Moon. Even thought the gap between the two calendars continues to increase, we do not have the authority to alter the calendar until a new Sanhedrin (religious high court) is reestablished and is widely recognized. While sanctification of the month according to observation is not practiced today it is important to carry out calculations and practice observing the New Moon in order to be ready for when the Sanhedrin is reestablished. Likewise, there is increasing involvement in the Temple, red heifer, etc. Of course, we are not intending to change the current calendar (this is a task for an authorized Sanhedrin) but just to increase involvement in and embellish the Torah.
In recent years, a number of individuals and groups have begun to observe the Moon each month to practice for the commandment of observing the Moon and for determining criteria for the limits of visibility. The is still plenty of room to improve on the existing criteria using observations and analyzing them in relation to physical, meteorological and physical parameters. We, the Israeli New Moon Society, are asking the public at large to join us by trying to observe the New Moon at the beginning of each month. The Israeli New Moon Society was founded for this purpose by Rabbi Dr. Nachum Rabinovitch, head of Yeshivat Birkat Moshe, Maale Adumim. The society works with the Institude for Kiddush Hachodesh Studies and includes scientists and rabbis from Universities, Yeshivot and elsewhere.
The Israeli New Moon Society presents the subject from the point of view of Rabbinical Orthodox Judaism. Those interested in the use of new Moon sighting from different religious viewpoints should refer to the Moslem, Karaite, Christian and religious ideas that have evolved from a combination of Christianity and Judaism.
The New Moon of 9th November 1999 as seen from the Mount of Olives
Photos: Roy Hoffman
1. To practice observing and to improve technique: For this purpose you need to know when and where to look. Diagrams, instructions and report forms are available from us, the Israeli New Moon Society.
2. To develop criteria for the limit of visibility: For this you have to find the Moon the moment it becomes visible to the naked eye. This requires expertise (and the use of binoculars helps a lot). Generally, an observer can develop the necessary skill after a few months of practice.
Photo Roy Hoffman 4th March 2003
Use one of our guides or use our software to help you and write down what you see on one of our forms. You should start searching for the Moon about five minutes before it is expected to appear. An observer that is looking hard sometimes tends to imagine that he has seen the Moon. To be sure that you really saw it, divert your gaze for a moment then look back to see if the Moon really is visible. Once the Moon has been found, one should ideally continue looking till the Moon fades or sets.
Photo: Jonathan Hoffman 9.12.1999
Using binoculars (diameter 50 mm) it is possible to see the Moon 10 to 15 minutes earlier than with the naked eye. In order to see the Moon with the naked eye, it is easiest to start with binoculars in order to locate it and then confirm the sighting with the naked eye. When the observation is difficult, binoculars can confirm that what was seen was the Moon rather than something else. For this purpose one should choose an appropriate pair of binoculars (7 to 20 x 30 to 80 mm).
It is best to find a place to look from where the horizon is unobstructed and where there are no bright lights from that direction. The height of the skyline should be less that 3°, i.e., do not stand in a valley.
Updated June 8th 2015 © Roy Hoffman and Tuvia Kaatz 2000-2015