Islamic Lunation Number

Overview

The Lunation Number is the number of New Moons since the epoch. There are several variations of this number.

This lunation number is used by the Hijri calendar. It uses the New Moon of 18 July 622 CE for its epoch, in this case denoted as Lunation 1.

Info

As lunations are important to many calendars and cultures, there are many competing standards.

The Islamic Lunation Number can be calculated by adding 17038 to the Lunation Number.

Accuracy

The lunation number is a simple calculation of time since the epoch divided by the average lunar cycle length. As the lunar cycle can vary by several hours, the time that the lunation number changes might not exactly match the current lunation. It is mostly intended to be used as an approximate reference rather than as a rigid definition of when the lunation has occurred.

Source

This calculation was sourced from Astronomical Algorithms (1991) by Jean Meeus.

More information can be found in its Wikipedia article.