Kiddush Levanah (Hebrew: קידוש לבנה ; trans. Sanctification Moon) is a Jewish ritual in which observant Jews recite a series of prayers shortly after Rosh Chodesh, though it may be done until the moon is full. The ritual is done at night when the moon is shining. The ritual may be performed from three days after the molad; others wait a full seven days from the molad. The latest time for Kiddush Levanah is mid-month, i.e., fourteen days, eighteen hours and twenty-two minutes (some authorities extend this limit to fifteen full days) after the molad.
It is customary to say Kiddush Levanah at the conclusion of Shabbat if possible. The moon must be visible and not totally covered by clouds and the ceremony is normally performed outside. While it is customary to say the prayer with the large crowd after the Saturday evening services, or at least with a minyan, it can be also said without a minyan and in the middle of the week. In places where cloudy or rainy weather is very common, many people will recite the blessing as soon as they see the moon for the first time after the "three days".
In the month of Tishrei, it is usually delayed until after the conclusion of Yom Kippur; others have a custom to say it specifically before Yom Kippur. In the month of Av, it is traditionally postponed to following the fast of Tisha B'Av, as the beginning of the month is a time of mourning and the prayer should be said in a spirit of joy. If a holiday falls on Sunday, Kiddush Levanah is delayed until after that day.
The source of the Kiddush Levana is in the Babylonian Talmud, (Sanhedrin 42a), Rabbi Yochanan taught that one who blesses the new moon, in its proper time, is regarded like one who greets the Shechinah (Divine Presence), as it is written in Exodus 12:2:, "This month (is to be for you the beginning of months..)”
This verse in Exodus 12:2 is the source of what is considered to be the first commandment in the Torah, which is to sanctify the new month, and is based on the lunar calendar. Although Kiddush levana is not the method of sanctifying the new month, we may be able to understand Rabbi Yochanan opinion that one who ‘blesses the new moon’, is also showing respect to the first commandment in the Torah, and therefore it is like greeting the Shechinah (Divine Presence).
It is customary to say the additional passages that were added to this blessing in the 16th century by Rabbi Yitzhak Luria.. These are Kabbalistic verses that are difficult to understand their deeper meaning.