Draft:Lunar calendar (Ancient Egypt)

The lunar calendars in Ancient Egypt, i.e., those among the simultaneously common Egyptian calendars, whose beginning of the month was always defined by the same moon phase, were  Bound lunar calendar in all documented cases. The beginning of a calendar year should preferably be the beginning of the Nile flood. It was associated very early with the appearance of the Sothis in the night sky. Therefore, the oldest documented calendars of Egypt also choose this event to determine the beginning of the year. This is also the case with the "Sothis lunar calendar".

The beginning of the month in Egypt was always considered to be the beginning of the non-visibility of the moon before sunrise, a month ended after the Old light. Thus, the Egyptian lunar calendars differed from those of many other cultures, in which a new month usually began with the new light.

Fundamentals of the calculation of time
General consensus is that the concepts of day and (lunar) month were developed before that of the year. A day always began with sunrise in Ancient Egypt. Thus, the events underlying the daily and monthly count were always before the day or month defined by this: The events usually fell in the 12th hour of the night, whereby each night, just like the light day, always had exactly 12 hours. The length of the hours changed accordingly with the seasons.
 * The night when the moon became a new moon before sunrise was the last in month.
 * The Heliacale rise of Sirius always took place at the end of the year. The New Year began after that with the beginning of the month.

Every hour, efforts were made to keep the course of the sun going in all the sun sanctuaries with ritual praises, but at least not to let a certain, processually conceived context of meaning be torn off. This context probably lies in the regularity. In Assmann 2005  it is then also stated: "Unlike in Mesopotamia and other divination cultures, the attention directed to the cosmos was not directed to the exceptions, but to the rules. In the cyclical regularity of his processes, the divinity of the cosmos was revealed to the Egyptian." So it is not surprising that, for example, the 15th day was always counted as the full moon day, regardless of the astronomical accuracy.

Variants of the lunar calendar
Since the beginning of the Egyptian calendar, the lunar calendar has also been further developed.

The original lunar calendar
The oldest documented mentions of lunar calendar dates are found from about 2350B.C. in the Pyramid Textsn. However, the use of astronomical records is already documented under King Wadji around 2880 B.C.

The original lunar calendar must have been based solely on observations. In any case, these observations included those of the Heliacalen rise of the Sothis. This event was called the "opener of the Year". This name was then also used for the 12th month in the "'Sothis year"', even if the event took place only after that. The first month of the New year then began after this event with the sunrise, before which the Moon was not visible again for the first time. This results in a leap year regulation based on observations, in which a 13th month was switched on in each case. In Parker 1950, the assumption was made that this happened exactly when the following month began less than 12 days after the Wepet-renpet event. In this case, the month that began after Wepet-renpet would be an intercalary 13. Month. With such a definition, he would have ensured that the event always fell in the month of the same name.

However, evidence that the beginning of a month has been calculated has not yet been found. As a result, however, an attempt was made by a number of scientists to conclude on the basis of astronomical calculations on exact calendar dates in the proleptic en  Julian Calendar. But in fact, this is not possible. Instead, errors in lunar observation must be assumed: Although Bradley E. Schaefer also states that "the currently great uncertainties in the prediction of lunar visibility do not allow a possible astronomical solution of absolute Egyptian chronology with lunar data", this does not prevent other scientists from continuing their research in this direction. In the meantime, the optical density and suspected historical dust pollution of the air are taken into account in the estimation of the visibility of the rise of Sirius.
 * Algorithms for calculating the visibility of the old lightthumb rules followed and proved to be incorrect in the majority of cases. Even better, more recent predictions are wrong in about 20%, that is, in 2-3 out of 12-13 cases.
 * Clouds could prevent the recognizability of the new moon.
 * Other sources of error may stand in the way of an estimation of the historical sighting.

In addition, the fact that the position of the lunar months in the Sidereal year fluctuates due to the length of the month and the repeated activation of an intercalary, thirteenth month stands in the way of general, narrowly limited information about the position of the months of the lunar calendar relative to our Gregorian calendar. Nevertheless, a rough estimate can be given: