One of the books that comes out once every ten years. It is one of the most significant foundational books of Greek literature and the most important in its field. It is a literary feat that inspires awe in the reader.

Its subject matter encompasses the calendrical systems of all peoples, from all times, of humanity. The authors of this study, who are associate professors of Astrophysics at the University of Athens, provide the reader with a scientific and captivating journey through history, religion, art, science, and global culture in general. Knowledge as the literature of our time.

The narration spans two volumes totaling 850 pages. The second volume examines: the saga of calendars in the united Roman Empire (Julian or old calendar) and Byzantium, the reform of the calendar during the time of Pope Gregory XIII (Gregorian calendar), the reactions that this specific reform provoked, the problem of determining Easter, the adoption of the Gregorian calendar by Christian peoples, the perpetual calendar (method for calculating the day of the week for any date), myths and legends about Santa Claus, the history and Greek folklore of the months of the year, the birth of Christ as the starting point of chronologies, new calendrical reforms, the calendars of the peoples of Northern Europe and Ireland, as well as the evolution of the calendar in Germany, calendars of other peoples (Armenian, Coptic, Ethiopian, Romani) and the efforts to compile a world calendar in the 19th and 20th centuries.

As in the first volume, all the calendars and calendrical developments are surrounded by oceans of information of historical, religious, artistic, and scientific interest. The study concludes with an appendix that examines the Julian period, the Vesalian year, the Indiction, the Solar cycle, the Easter Full Moon, the astronomical phenomena of precession and nutation, and the date of Easter from an astronomical perspective.

Also published are: a chronology of world events from 6000 B.C. to the present, a summary of chronological eras, a 251-year calendar (1800-2050 A.D.), a perpetual calendar of 50 years, bibliography, and an index. An acquisition of immeasurable epistemological value.