New moon

[2] At this phase, the lunar disk is not visible to the naked eye, except when it is silhouetted against the Sun during a solar eclipse.

[3] This thin waxing crescent is briefly and faintly visible as the Moon gets lower in the western sky after sunset.

The precise time and even the date of the appearance of the new moon by this definition will be influenced by the geographical location of the observer.

In the Chinese calendar, the beginning of the month is marked by the last visible crescent of a waning Moon.

[5] However, the length of any one synodic month can vary from 29.26 to 29.80 days (12.96 hours) due to the perturbing effects of the Sun's gravity on the Moon's eccentric orbit.

[12] Since the Babylonian captivity, this month is called Nisan, and it is calculated based on mathematical rules designed to ensure that festivals are observed in their traditional season.

[13] This fixed lunisolar calendar follows rules introduced by Hillel II and refined until the ninth century.

This calculation makes use of a mean lunation length used by Ptolemy and handed down from Babylonians, which is still very accurate: ca.

These fifteen dates are divided evenly into five categories: Nanda, Bhadra', Jaya, Rikta, and Purna, which are cycled through in that order.

In Saudi Arabia, the new King Abdullah Centre for Crescent Observations and Astronomy in Mecca has a clock for addressing this as an international scientific project.

In the Baháʼí Faith, effective from 2015 onwards, the "Twin Holy Birthdays", refer to two successive holy days in the Baháʼí calendar (the birth of the Báb and the birth of Bahá'u'lláh), will be observed on the first and the second day following the occurrence of the eighth new moon after Naw-Rúz (Baháʼí New Year), as determined in advance by astronomical tables using Tehran as the point of reference.