In the Middle Ages, the study of the measure of time was first viewed as prying too deeply into God’s own affairs and later thought of as a lowly, mechanical study, unworthy of serious contemplation.As a result, it wasn’t until 1582, by which time Caesar’s calendar had drifted a full 10 days off course, that Pope Gregory XIII (1502 - 1585) finally reformed the Julian calendar.Since the lunar calendar was 10 or 11 days shorter than the solar year, a 13th month (called Thoth) was Sirius), when it could be observed on the eastern horizon just before dawn in midsummer; the timing of this observation would determine whether or not the intercalary month would be employed.The Egyptian civil calendar was introduced later, presumably for more-precise administrative and accounting purposes.They used the seasonal appearance of the star Sirius (Sothis);…The Egyptian month began with the new moon—reckoned from the first morning after the waning crescent had become invisible—and was named after the major festival celebrated within it.Fires were extinguished and the population refrained from eating hot food. It is a purely solar calendar, with a cycle of leap days in a year cycle designed to keep the duration of the year aligned with the solar year. Because the length of the lunar month is not an even fraction of the length of the tropical year , a purely lunar calendar quickly drifts against the seasons, which do not vary much near the equator.
The ancient Egyptians originally employed a calendar based upon the Moon, and, like many peoples throughout the world, they regulated their lunar calendar by means of the guidance of a sidereal calendar.
According to the Muslim lunar calendar, dating from Muhammad's Hijra (flight or emigration) from Mecca, it is now ah 1430.
Persians, Mayans, Jains, even Freemasons, all have their own eras.
It consisted of 365 days organized into 12 months of 30 days each, with an additional five epagomenal days (days occurring outside the ordinary temporal construct) grouped at the end of the year.
There was apparently no attempt to introduce a leap-year day to compensate for the slippage of one day every four years; as a result, the civil calendar slowly rotated through the seasons, making a complete cycle through the solar calendar after 1,460 years (referred to as a a schematized 25-year lunar calendar was apparently devised on the pattern of the civil calendar, in order to determine within accurate limits the beginning of lunar months without regard to actual observation of the moon’s waning crescent.