Lesson 9. Chronology Learning tasks: by completing this unit of study, the student will be able to: ¾ Define Chronology and to highlight the key moments in its evolution as science. ¾ Identify main elements of timeline (day, hour, week, month, year). ¾ Retain some elementary notions about the calendar. I. Definition; The evolution of Chronology as science Chronology from Latin chronologia, from Ancient Greek χρόνος, chronos = time, and ­λογία, ­logia) is the Auxiliary Science of History which deal with the measuring and dividing of time, therefore with accurate dating of historical events to determine their sequence. Chronology has two major branches: Astronomical Chronology, a technical method of dating events or artifacts that are associated with astronomical phenomena, and Historical Chronology, to achieve timelines: national, universal, of different institutions and of their leaders, of various historical events. There were two systems to highlight the time: the astronomical system and the civil system, of which there were some differences. But, both systems were based on revolution movements of the Earth, the Moon and Sun. In Antiquity, historiography has shown a constant concern for establishing accurate data of events narrated, but made after the dating system used at that time. In XV­XVIII centuries, Chronology make important steps in its evolution as a scientific discipline. The problematic of Chronology began with the controversy between Joseph Justus Scaliger (August 5, 1540, Agen‐January 21, 1609, Leiden) and Denis Pétau (August 21, 1583 – December 11, 1652), which gave to Benedictines the opportunity to undertake the difficult task to clarify the research field of Chronology. They needed a long time until to draft critical chronological lists and to clarify old dating systems. Their treatise, L’Art verifier les dates (Paris, 1750), underpins to all manuals of Chronology who were written afterwards in almost every country. In the nineteenth century, the progress of Chronology is due largely achievements in astronomy and mathematics. Among the many contributions of the twentieth century, in the field of Chronology, mention those belonging to: Eugène Cavaignac, Chronologie de l’histoire mondiale (Paris, 1925), Paul Couderc, Le Calendrier (Paris, 1946) and Venance Grumel, La chronologie (Paris, 1958). * Daniel Flaut, Introduction to the Auxiliary Sciences of History II. Main elements of timeline (day, hour, week, month, year) a) Day Also called civil day is the period of time, the calendar day, of 24 hours' duration reckoned from one midnight to the next. In Astronomy, day is a division of time equal to 24 hours and representing the average length of the period during which the earth makes one rotation on its axis. In Antiquity, Babylonians believed that the day begins at sunrise, ancient Egyptians, Chinese and Romans at midnight and Greeks and Arabs at sunset. In 1925, astronomers have determined that the astronomical day begins at midnight, after 12 p.m. In this way, the start of the astronomical day coincides with the start of the civil day. b) Hour In Antiquity, Babylonians divided day into smaller units of time, the gnomon devised for the light of the day on which they divided into six equal fractions. Hourglasses were used to measure time during night‐time in the absence of sunlight. Romans were the ones who divided the civil day into 24 equal parts, called horae (hours). In the twelfth century was invented pendulum and in the fifteenth and sixteenth centuries were created clocks which were placed in the center of each town. With sounds of bells, clocks announced hour at every 12 hours and later by four times per day at an interval of six hours. The first pocket watch powered with a spiral was called ”Nurnberg egg” (because of its size and shape). Is was constructed around 1500 by Peter Henlein, a Nurnberger watchmaker. Like a circle, the Earth has 360 degrees. The ecuator is the widest circumference of the globe. In 1884 an American engineer divided the equator in 24 equal parts with 24 imaginary lines, also called meridians, running vertically around the globe. Meridians meet at the poles and are widest apart at the equator. Zero degrees longitude (0°) is called the prime meridian, which runs through the Royal Greenwich Observatory in Greenwich, England. The degrees of longitude run 180° east and 180° west from the prime meridian. The prime meridian divides the globe into the Western and Eastern hemispheres. The Earth's time zones are measured from the prime meridian. The time at 0° is called Universal Time (UT) or Greenwich Mean Time (GMT). With the Greenwich meridian as the starting point, each 15° east and west marks a new time zone. The 24 time zones extend east and west around the globe for 180° to the International Date Line. Since 180°runs through several countries, it would divide those countries not simply into two different time zones, but into two different calendar days. c) Week Babylonians and Jews were the first who reckoned the time in weeks. At Jews, the week had seven days, then was taken over by Greeks and even by Romans. The origin of the seven days is related to the motion of the Moon. A week is a phase of the Moon (4 weeks = 4 phases of the Moon). Designation of days grouped into weeks starts from the first century BC. From Romans, the week (with seven days) was taken over by Germanic peoples who replaced names of Roman divinities with names of German divinities. Slavs designated 2 Daniel Flaut, Introduction to the Auxiliary Sciences of History weekdays after their number inside the cycle. The week is a period of time intermediate between the short time and the long time. d) Month People have sought a longer unit of time which they found in the motion of the Moon. The lunar month is the 29.53 days it takes to go from one new moon to the next. During the lunar month, the Moon goes through all its phases (new moon, first quarter moon, full moon, third quarter moon). In Antiquity ‐ when the month had 29 days ‐ were observed at one point that the beginning of the civil month no longer corresponded with the appearance of the new moon on the sky and was added one day. The month thus became of 30 days, but again it was a mismatch, so that was adopted an alternating of months of 29 and 30 days. The result was a year of 354 or 355 days, called lunar year. It was used by Babylonians, Chinese, Greeks, Romans and Arabs. Medieval Muslims have not changed the lunar year but they introduced a new starting date, Hegira (622 AD). e) Year In antiquity, each people had its own system of numbering of years. In Egypt the timeline was made after the reigns of pharaohs. Greeks were numbered years after magistrates or after winners of the games of Olympia. Romans numbered years starting from the date of the founding of Rome. Byzantines, Slavs and Romanians began counting the years from 5508 (genesis). A year (from Old English gēar) is the orbital period of the Earth moving around the Sun. In the Middle Ages there was the belief that the Earth is the center of the Universe and that the Sun revolves around the Earth. In 1512, the Polish astronomer Nicolaus Copernicus (Mikolaj Kopernik) elaborated the theory that the Sun is at rest near the center of the Universe, and that the Earth, spinning on its axis once daily, revolves annually around the Sun (the heliocentric system). The new theory was adopted unanimously by scientists only in the eighteenth century. The tropical year is the actual time for the Earth to go around the Sun. The length of a tropical year is 365 days, 5 hours, 48 minutes, 46 seconds. He is shorter than the sidereal year which is the time for the Earth to circle the Sun relative to a fixed celestial object, such as a star (365 days, 6 hours, 9 minutes, 9.5 seconds). * III. The calendar The purpose of the calendar is to reckon past or future time. The earliest calendars have been strongly influenced by the geographical location of the people who made them. Over the time were used three basic types of calendars: ­Solar calendar. It is the oldest known type of calendar, used by Egyptians since 6000 BC. It contained 12 months of 30 days with 5 days additional and result a year with 365 days. This calendar had one day difference once every 4 years. ­Lunisolar calendar. It was based on the principle that the first day of each lunar months must coincide with the appearance of the new moon on the sky. Following calendars are lunisolar: the ancient Hellenic, Coligny and Babylonian 3 Daniel Flaut, Introduction to the Auxiliary Sciences of History calendars; the traditional Chinese, Japanese, Vietnamese, Mongolian and Korean calendars; the Hebrew, Buddhist, Hindu lunisolar, Burmese and Tibetan calendars. Lunisolar calendar was based on the movement of the Moon for 12 months and a month had 28‐30 days. It was used by Babylonians at about 5000 BC. ‐Lunar calendar. It was based on cycles of the lunar phase. This calendar was used by Arabs and Muslims in general. It contained 12 months of 29‐30 days and result a year with 354 days. The Julian Calendar Romans were the ones who perfected the solar calendar. The Julian calendar was introduced by Julius Caesar in 45 BC. He consulted with an Alexandrian astronomer named Sosigenes and created a more regulated civil calendar based entirely on the Earth's revolutions around the sun. The Roman calendar consisted of 12 months for a total of 355 days.