The five books of Enoch are a collection of books written in Semitic languages, and often grouped together as the 'Book of Enoch,' or '1st Enoch.' The books were likely written at different points in time and different Semitic languages. The first book was the Book of the Watchers, which is generally considered to be the oldest book in the collection, however, the age of the book is debated. The book is now known to have originated long before Christianity since the discovery of the Dead Sea Scrolls, however, was lost for well over a thousand years to Europeans, and assumed to be a Christian-era work when the Europeans rediscovered it in Ethiopia. The five books of Enoch only survive in Ge'ez, the classical language of Ethiopia, however, do not survive intact, and some sections of text do not survive. The Astronomical Book explains a very different version of reality from the one that most people believe in today: a flat world with a physical sky above it. In this other world, the sun, moon, and stars all enter the space under the sky through portals at the east edge of the world and exit through the portals at the western edge of the world. The Astronomical Book attempts to explain the movement of the sun, moon, and winds, and is sometimes referred to as the Enochian Calendar, as it tried to explain the way the days, months, and years pass over time, and how the winds changed through the year. The world described is similar to the ancient Babylonian world view, which many ancient cultures inherited and used until the Greek philosopher Eratosthenes proposed the alternate concept that the world was spherical around 240 BC. The two world-systems were debated until the Imperial Church of Rome officially endorsed the flat Earth, which became the standard European world-view until the time of Copernicus. The Astronomical Book does not have many unique terms or descriptions of events to date it by like the other books of Enoch. There are many unique names found in the Astronomical Book but most cannot be traced back to a specific language or culture, and are therefore not useful for dating the text. The surviving fragments found among the Dead Sea scrolls are accepted as dating back to the 3rd-century BC, however, the book could be significantly older. The names of the sun in chapter 7 could indicate that some of the text originated in the Old Kingdom of Egypt. The names are listed as Orjares and Tomas are possibly based on the Egyptian terms Her-ur and Atum, which were pronounced as herwer and tmw respectively, and were both solar gods. Her-ur was the national god in the first few dynasties of the Old Kingdom, however, had been replaced by the sun-god Ra by the 5th Dynasty. By the Middle Kingdom, Her-ur was replaced by Osiris as the husband of Isis and the father of Horus the younger. If the name Orjares is a corruption of Her-ur, the date of the original text would most-likely date back to before the 5th-Dynasty, and almost certainly before the Middle Kingdom. On the other hand, Atum continued to be worshiped until the New Kingdom, and based on the Letter of Aristeas and the Pithom Stele, was believed to have been Moses' original god by some Jews and Greeks at the time the Septuagint was translated at the Library of Alexandria.