The Ten Commandments known as the Decalogue, are a set of biblical principles relating to ethics and worship, which play a fundamental role in Judaism and Christianity. The commandments include instructions to worship only God, to honour one's parents, to keep the sabbath day holy, as well as prohibitions against idolatry, murder, theft and coveting. Different religious groups follow different traditions for numbering them; the Ten Commandments appear twice in the books of Exodus and Deuteronomy. Modern scholarship has found influences in Hittite and Mesopotamian laws and treaties, but is divided over when the Ten Commandments were written and who wrote them. In biblical Hebrew, the Ten Commandments are called עשרת הדברים and in Mishnaic Hebrew עשרת הדברות, both translatable as "the ten words", "the ten sayings", or "the ten matters"; the Tyndale and Coverdale English biblical translations used "ten verses". The Geneva Bible used "tenne commandements", followed by the Bishops' Bible and the Authorized Version as "ten commandments".
Most major English versions use "commandments."The English name "Decalogue" is derived from Greek δεκάλογος, the latter meaning and referring to the Greek translation δέκα λόγους, deka logous, "ten words", found in the Septuagint at Exodus 34:28 and Deuteronomy 10:4. The stone tablets, as opposed to the commandments inscribed on them, are called לוחות הברית, Lukhot HaBrit, meaning "the tablets of the covenant". Different religious traditions divide the seventeen verses of Exodus 20:1–17 and their parallels at Deuteronomy 5:4–21 into ten "commandments" or "sayings" in different ways, shown in the table below; some suggest. All scripture quotes above are from the King James Version. Click on verses at top of columns for other versions. Traditions: LXX: Septuagint followed by Orthodox Christians. P: Philo, same as the Septuagint, but with the prohibitions on killing and adultery reversed. S: Samaritan Pentateuch, with an additional commandment about Mount Gerizim as 10th. T: Jewish Talmud, makes the "prologue" the first "saying" or "matter" and combines the prohibition on worshiping deities other than Yahweh with the prohibition on idolatry.
A: Augustine follows the Talmud in combining verses 3–6, but omits the prologue as a commandment and divides the prohibition on coveting in two and following the word order of Deuteronomy 5:21 rather than Exodus 20:17. C: Catechism of the Catholic Church follows Augustine. L: Lutherans follow Luther's Large Catechism, which follows Augustine but subordinates the prohibition of images to the sovereignty of God in the First Commandment and uses the word order of Exodus 20:17 rather than Deuteronomy 5:21 for the ninth and tenth commandments. R: Reformed Christians follow John Calvin's Institutes of the Christian Religion, which follows the Septuagint; the biblical narrative of the revelation at Sinai begins in Exodus 19 after the arrival of the children of Israel at Mount Sinai. On the morning of the third day of their encampment, "there were thunders and lightnings, a thick cloud upon the mount, the voice of the trumpet exceeding loud", the people assembled at the base of the mount. After "the LORD came down upon mount Sinai", Moses went up and returned and prepared the people, in Exodus 20 "God spoke" to all the people the words of the covenant, that is, the "ten commandments" as it is written.
Modern biblical scholarship differs as to whether Exodus 19-20 describes the people of Israel as having directly heard all or some of the decalogue, or whether the laws are only passed to them through Moses. The people were afraid to hear more and moved "afar off", Moses responded with "Fear not." He drew near the "thick darkness" where "the presence of the Lord" was to hear the additional statutes and "judgments", all which he "wrote" in the "book of the covenant" which he read to the people the next morning, they agreed to be obedient and do all that the LORD had said. Moses escorted a select group consisting of Aaron and Abihu, "seventy of the elders of Israel" to a location on the mount where they worshipped "afar off" and they "saw the God of Israel" above a "paved work" like clear sapphire stone, and the LORD said unto Moses, Come up to me into the mount, be there: and I will give thee tablets of stone, a law, commandments which I have written. 13 And Moses rose up, his minister Joshua: and Moses went up into the mount of God.
The mount was covered by the cloud for six days, on the seventh day Moses went into the midst of the cloud and was "in the mount forty days and forty nights." And Moses said, "the LORD delivered unto me two tablets of stone written with the finger of God. Before the full forty days expired, the children of Israel collectively decided that something had happened to Moses, compelled Aaron to fashion a golden calf, he "built an altar before it" and the people "worshipped" the calf. After the full forty days and Joshua came down from the mountain with the tablets of stone: "And it came to pass, as soon as he came nigh unto the camp, that he saw the calf, the dancing: and Moses' anger waxed hot, he cast the tablets out of his hands, brak
The Hebrew or Jewish calendar is a lunisolar calendar used today predominantly for Jewish religious observances. It determines the dates for Jewish holidays and the appropriate public reading of Torah portions and daily Psalm readings, among many ceremonial uses. In Israel, it is used for religious purposes, provides a time frame for agriculture and is an official calendar for civil purposes, although the latter usage has been declining in favor of the Gregorian calendar; the present Hebrew calendar is the product including a Babylonian influence. Until the Tannaitic period, the calendar employed a new crescent moon, with an additional month added every two or three years to correct for the difference between twelve lunar months and the solar year; the year in which it was added was based on observation of natural agriculture-related events in ancient Israel. Through the Amoraic period and into the Geonic period, this system was displaced by the mathematical rules used today; the principles and rules were codified by Maimonides in the Mishneh Torah in the 12th century.
Maimonides' work replaced counting "years since the destruction of the Temple" with the modern creation-era Anno Mundi. The Hebrew lunar year is about eleven days shorter than the solar year and uses the 19-year Metonic cycle to bring it into line with the solar year, with the addition of an intercalary month every two or three years, for a total of seven times per 19 years. With this intercalation, the average Hebrew calendar year is longer by about 6 minutes and 40 seconds than the current mean tropical year, so that every 217 years the Hebrew calendar will fall a day behind the current mean tropical year; the era used. As with Anno Domini, the words or abbreviation for Anno Mundi for the era should properly precede the date rather than follow it. AM 5779 began at sunset on 9 September 2018 and will end at sunset on 29 September 2019; the Jewish day is of no fixed length. The Jewish day is modeled on the reference to "...there was evening and there was morning..." in the creation account in the first chapter of Genesis.
Based on the classic rabbinic interpretation of this text, a day in the rabbinic Hebrew calendar runs from sunset to the next sunset. Halachically, a day ends and a new one starts when three stars are visible in the sky; the time between true sunset and the time when the three stars are visible is known as'bein hashmashot', there are differences of opinion as to which day it falls into for some uses. This may be relevant, for example, in determining the date of birth of a child born during that gap. There is no clock in the Jewish scheme. Though the civil clock, including the one in use in Israel, incorporates local adoptions of various conventions such as time zones, standard times and daylight saving, these have no place in the Jewish scheme; the civil clock is used only as a reference point – in expressions such as: "Shabbat starts at...". The steady progression of sunset around the world and seasonal changes results in gradual civil time changes from one day to the next based on observable astronomical phenomena and not on man-made laws and conventions.
In Judaism, an hour is defined as 1/12 of the time from sunrise to sunset, so, during the winter, an hour can be much less than 60 minutes, during the summer, it can be much more than 60 minutes. This proportional hour is known as a sha'ah z'manit. A Jewish hour is divided into parts. A part is 1/18 minute; the ultimate ancestor of the helek was a small Babylonian time period called a barleycorn, itself equal to 1/72 of a Babylonian time degree. These measures are not used for everyday purposes. Instead of the international date line convention, there are varying opinions as to where the day changes. One opinion uses the antimeridian of Jerusalem. Other opinions exist as well; the weekdays proceed to Saturday, Shabbat. Since some calculations use division, a remainder of 0 signifies Saturday. While calculations of days and years are based on fixed hours equal to 1/24 of a day, the beginning of each halachic day is based on the local time of sunset; the end of the Shabbat and other Jewish holidays is based on nightfall which occurs some amount of time 42 to 72 minutes, after sunset.
According to Maimonides, nightfall occurs. By the 17th century, this had become three-second-magnitude stars; the modern definition is when the center of the sun is 7° below the geometric horizon, somewhat than civil twilight at 6°. The beginning of the daytime portion of each day is determined both by sunrise. Most halachic times are based on some combination of these four times and vary from day to day throughout the year and vary depending on location; the daytime hours are divided into Sha'oth Zemaniyoth or "Halachic hours" by taking the time between sunrise and sunset or between dawn and nightfall and dividing it into 12 equal hours. The nighttime hours are s
Johns Hopkins University
Johns Hopkins University is a private research university in Baltimore, Maryland. Founded in 1876, the university was named for its first benefactor, the American entrepreneur and philanthropist Johns Hopkins, his $7 million bequest —of which half financed the establishment of Johns Hopkins Hospital—was the largest philanthropic gift in the history of the United States up to that time. Daniel Coit Gilman, inaugurated as the institution's first president on February 22, 1876, led the university to revolutionize higher education in the U. S. by integrating teaching and research. Adopting the concept of a graduate school from Germany's ancient Heidelberg University, Johns Hopkins University is considered the first research university in the United States. Over the course of several decades, the university has led all U. S. universities in annual research and development expenditures. In fiscal year 2016, Johns Hopkins spent nearly $2.5 billion on research. Johns Hopkins is organized into 10 divisions on campuses in Maryland and Washington, D.
C. with international centers in Italy and Singapore. The two undergraduate divisions, the Zanvyl Krieger School of Arts and Sciences and the Whiting School of Engineering, are located on the Homewood campus in Baltimore's Charles Village neighborhood; the medical school, the nursing school, the Bloomberg School of Public Health are located on the Medical Institutions campus in East Baltimore. The university consists of the Peabody Institute, the Applied Physics Laboratory, the Paul H. Nitze School of Advanced International Studies, the School of Education, the Carey Business School, various other facilities. Johns Hopkins was a founding member of the American Association of Universities. Johns Hopkins University is cited as among the world's top universities; the university is ranked 10th among undergraduate programs at National Universities in U. S. News & World Report latest rankings, 10th among global universities by U. S. News & World Report in its 2019 rankings, as well as 12th globally in the Times Higher Education World University Rankings.
Over the course of more than 140 years, 37 Nobel laureates and 1 Fields Medalist have been affiliated with Johns Hopkins. Founded in 1883, the Blue Jays men's lacrosse team has captured 44 national titles and joined the Big Ten Conference as an affiliate member in 2014. On his death in 1873, Johns Hopkins, a Quaker entrepreneur and childless bachelor, bequeathed $7 million to fund a hospital and university in Baltimore, Maryland. At that time this fortune, generated from the Baltimore and Ohio Railroad, was the largest philanthropic gift in the history of the United States; the first name of philanthropist Johns Hopkins is the surname of his great-grandmother, Margaret Johns, who married Gerard Hopkins. They named their son Johns Hopkins. Samuel named one of his sons for his father and that son would become the university's benefactor. Milton Eisenhower, a former university president, once spoke at a convention in Pittsburgh where the Master of Ceremonies introduced him as "President of John Hopkins."
Eisenhower retorted that he was "glad to be here in Pittburgh." The original board opted for an novel university model dedicated to the discovery of knowledge at an advanced level, extending that of contemporary Germany. Building on the Humboldtian model of higher education, the German education model of Wilhelm von Humboldt, it became dedicated to research. Johns Hopkins thereby became the model of the modern research university in the United States, its success shifted higher education in the United States from a focus on teaching revealed and/or applied knowledge to the scientific discovery of new knowledge. The trustees worked alongside four notable university presidents – Charles W. Eliot of Harvard, Andrew D. White of Cornell, Noah Porter of Yale College and James B. Angell of Michigan, they each vouched for Daniel Coit Gilman to lead the new University and he became the university's first president. Gilman, a Yale-educated scholar, had been serving as president of the University of California prior to this appointment.
In preparation for the university's founding, Gilman visited University of Freiburg and other German universities. Gilman launched what many at the time considered an audacious and unprecedented academic experiment to merge teaching and research, he dismissed the idea that the two were mutually exclusive: "The best teachers are those who are free and willing to make original researches in the library and the laboratory," he stated. To implement his plan, Gilman recruited internationally known luminaries such as the mathematician James Joseph Sylvester. Gilman focused on the expansion of graduate support of faculty research; the new university fused advanced scholarship with such professional schools as medicine and engineering. Hopkins became the national trendsetter in doctoral programs and the host for numerous scholarly journals and associations; the Johns Hopkins University Press, founded in 1878, is the oldest American university press in continuous operation. With the completion of Johns Hopkins Hospital in 1889 and the medical school in 1893, the university's research-focused mode of instruction soon began attracting world-renowned faculty members who would become major figures in the emerging field of acad
The traditional China calendar, or Former Calendar, Traditional Calendar or Lunar Calendar, is a lunisolar calendar which reckons years and days according to astronomical phenomena. It is defined by GB/T 33661-2017, "Calculation and promulgation of the Chinese calendar", issued by the Standardisation Administration of China on 12 May 2017. Although modern day China uses the Gregorian calendar, the traditional Chinese calendar governs holidays in China and in overseas Chinese communities, it lists the dates of traditional Chinese holidays and guides people in selecting auspicious days for weddings, moving, or starting a business. Like Chinese characters, variants of this calendar are used in different parts of the Chinese cultural sphere. Korea and the Ryukyu Islands adopted the calendar, it evolved into Korean and Ryukyuan calendars; the main difference from the traditional Chinese calendar is the use of different meridians, which leads to some astronomical events—and calendar events based on them—falling on different dates.
The traditional Japanese calendar derived from the Chinese calendar, but its official use in Japan was abolished in 1873 as part of reforms after the Meiji Restoration. Calendars in Mongolia and Tibet have absorbed elements of the traditional Chinese calendar, but are not direct descendants of it. Days begin and end at midnight, months begin on the day of the new moon. Years begin on the second new moon after the winter solstice. Solar terms govern the end of each month. Written versions in ancient China included stems and branches of the year and the names of each month, including leap months as needed. Characters indicated whether a month was short; the traditional Chinese calendar was developed between 771 and 476 BC, during the Spring and Autumn period of the Eastern Zhou dynasty. Before the Zhou dynasty, solar calendars were used. One version of the solar calendar is the five-elements calendar. A 365-day year was divided into five phases of 73 days, with each phase corresponding to a Day 1 Wu Xing element.
A phase began followed by six 12-day weeks. Each phase consisted of two three-week months. Years began followed by a bǐngzǐ day and a 72-day fire phase. Other days were tracked using the Yellow River Map. Another version is a four-quarters calendar. Weeks were ten days long, with one month consisting of three weeks. A year had 12 months, with a ten-day week intercalated in summer as needed to keep up with the tropical year; the 10 Heavenly Stems and 12 Earthly Branches were used to mark days. A third version is the balanced calendar. A year was 365.25 days, a month was 29.5 days. After every 16th month, a half-month was intercalated. According to oracle bone records, the Shang dynasty calendar was a balanced calendar with 12 to 14 months in a year; the first lunisolar calendar was the Zhou calendar, introduced under the Zhou dynasty. This calendar set the beginning of the year at the day of the new moon before the winter solstice, it set the shàngyuán as the winter solstice of a dīngsì year, making the year it was introduced around 2,758,130.
Several competing lunisolar calendars were introduced by states fighting Zhou control during the Warring States period. The state of Lu issued its own Lu calendar. Jin issued the Xia calendar in AD 102, with a year beginning on the day of the new moon nearest the March equinox. Qin issued the Zhuanxu calendar, with a year beginning on the day of the new moon nearest the winter solstice. Song's Yin calendar began its year on the day of the new moon after the winter solstice; these calendars are known as the six ancient calendars, or quarter-remainder calendars, since all calculate a year as 365 1⁄4 days long. Months begin on the day of the new moon, a year has 12 or 13 months. Intercalary months are added to the end of the year; the Qiang and Dai calendars are modern versions of the Zhuanxu calendar, used by mountain peoples. After Qin Shi Huang unified China under the Qin dynasty in 221 BC, the Qin calendar was introduced, it followed most of the rules governing the Zhuanxu calendar, but the month order was that of the Xia calendar.
The intercalary month, known as the second Jiǔyuè, was placed at the end of the year. The Qin calendar was used into the Han dynasty. Emperor Wu of Han r. 141 – 87 BC introduced reforms halfway through his reign. His Taichu Calendar defined a solar year as 365 385⁄1539 days, the lunar month was 29 43⁄81 days; this calendar introduced the 24 solar terms. Solar terms were paired, with the 12 combined periods known as climate terms; the first solar term of the period was known as a pre-climate, the second was a mid-climate. Months were named for the mid-climat
The Ethiopian calendar or Eritrean calendar is the principal calendar used in Ethiopia and serves as the liturgical year for Christians in Eritrea and Ethiopia belonging to the Eritrean Orthodox Tewahedo Church, Ethiopian Orthodox Tewahedo Church, Eastern Catholic Churches, the Coptic Orthodox Church of Alexandria, Ethiopian-Eritrean Evangelicalism. It is a solar calendar which in turn derives from the Egyptian calendar, but like the Julian calendar, it adds a leap day every four years without exception, begins the year on August 29 or August 30 in the Julian calendar. A gap of 7–8 years between the Ethiopian and Gregorian calendars results from an alternative calculation in determining the date of the Annunciation. Like the Coptic calendar, the Ethiopic calendar has 12 months of 30 days plus 5 or 6 epagomenal days, which comprise a thirteenth month; the Ethiopian months begin on the same days as those of the Coptic calendar, but their names are in Ge'ez. A 6th epagomenal day is added every 4 years, without exception, on August 29 of the Julian calendar, 6 months before the corresponding Julian leap day.
Thus the first day of the Ethiopian year, 1 Mäskäräm, for years between 1900 and 2099, is September 11. However, it falls on September 12 in years before the Gregorian leap year. Enkutatash is the word for the Ethiopian New Year in Amharic, the official language of Ethiopia, while it is called Ri'se Awde Amet in Ge'ez, the term preferred by the Ethiopian & Eritrean Orthodox Tewahedo Churchs, it occurs on September 11th in the Gregorian Calendar. The Ethiopian Calendar Year 1998 Amätä Məhrät began on the Gregorian Calendar Year on September 11th, 2005. However, the Ethiopian Years 1992 and 1996 began on the Gregorian Dates of'September 12th 1999' and'2003' respectively; this date correspondence applies for the Gregorian years 1900 to 2099. The Ethiopian leap year is every four without exception, while Gregorian centurial years are only leap years when divisible by 400; as the Gregorian year 2000 is a leap year, the current correspondence lasts two centuries instead. The start of the Ethiopian year falls on August 30th.
This date corresponds to the Old-Style Julian Calendar. This deviation between the Julian and the Gregorian Calendar will increase with the passing of the time. You can observe the real start date in the future centuries in a Gregorian to Ethiopian Date Converter. To indicate the year and followers of the Eritrean churches today use the Incarnation Era, which dates from the Annunciation or Incarnation of Jesus on March 25, AD 9, as calculated by Annianus of Alexandria c. 400. Meanwhile, Europeans adopted the calculations made by Dionysius Exiguus in AD 525 instead, which placed the Annunciation 8 years earlier than had Annianus; this causes the Ethiopian year number to be 8 years less than the Gregorian year number from January 1 until September 10 or 11 7 years less for the remainder of the Gregorian year. In the past, a number of other eras for numbering years were widely used in Ethiopia and the Kingdom of Aksum; the most important era – once used by the Eastern Christianity, still used by the Coptic Orthodox Church of Alexandria – was the Era of Martyrs known as the Diocletian Era, or the era of Diocletian and the Martyrs, whose first year began on August 29, 284.
Respective to the Gregorian and Julian New Year's Days, 31⁄2 to 4 months the difference between the Era of Martyrs and the Anni Domini is 285 years. This is because in AD 525, Dionysius Exiguus decided to add 15 Metonic cycles to the existing 13 Metonic cycles of the Diocletian Era to obtain an entire 532 year medieval Easter cycle, whose first cycle ended with the year Era of Martyrs 247 equal to year DXXXI, it is because 532 is the product of the Metonic cycle of 19 years and the solar cycle of 28 years. Around AD 400, an Alexandrine monk called Panodoros fixed the Alexandrian Era, the date of creation, on 29 August 5493 BC. After the 6th century AD, the era was used by Ethiopian chronologists; the twelfth 532 year-cycle of this era began on 29 August AD 360, so 4×19 years after the Era of Martyrs. Bishop Anianos preferred the Annunciation style as 25 March, thus he shifted the Panodoros era by about six months, to begin on 25 March 5492 BC. In the Ethiopian calendar this was equivalent to 15 Magabit 5501 B.
C.. The Anno Mundi era remained in usage until the late 19th century; the 4 year leap-year cycle is associated with the four Evangelists: the first year after an Ethiopian leap year is named the John-year, followed by the Matthew-year, the Mark-year. The year with the 6th epagomenal day is traditionally designated as the Luke-year. There are no exceptions to the 4 year leap-year cycle, like the Julian calendar but unlike the Gregorian calendar; these dates are valid only from March 1900 to February 2100. This is because 1900 and 2100 are not leap years in the Gregorian calendar, while they are still leap year
Astronomy is a natural science that studies celestial objects and phenomena. It applies mathematics and chemistry in an effort to explain the origin of those objects and phenomena and their evolution. Objects of interest include planets, stars, nebulae and comets. More all phenomena that originate outside Earth's atmosphere are within the purview of astronomy. A related but distinct subject is physical cosmology, the study of the Universe as a whole. Astronomy is one of the oldest of the natural sciences; the early civilizations in recorded history, such as the Babylonians, Indians, Nubians, Chinese and many ancient indigenous peoples of the Americas, performed methodical observations of the night sky. Astronomy has included disciplines as diverse as astrometry, celestial navigation, observational astronomy, the making of calendars, but professional astronomy is now considered to be synonymous with astrophysics. Professional astronomy is split into theoretical branches. Observational astronomy is focused on acquiring data from observations of astronomical objects, analyzed using basic principles of physics.
Theoretical astronomy is oriented toward the development of computer or analytical models to describe astronomical objects and phenomena. The two fields complement each other, with theoretical astronomy seeking to explain observational results and observations being used to confirm theoretical results. Astronomy is one of the few sciences in which amateurs still play an active role in the discovery and observation of transient events. Amateur astronomers have made and contributed to many important astronomical discoveries, such as finding new comets. Astronomy means "law of the stars". Astronomy should not be confused with astrology, the belief system which claims that human affairs are correlated with the positions of celestial objects. Although the two fields share a common origin, they are now distinct. Both of the terms "astronomy" and "astrophysics" may be used to refer to the same subject. Based on strict dictionary definitions, "astronomy" refers to "the study of objects and matter outside the Earth's atmosphere and of their physical and chemical properties," while "astrophysics" refers to the branch of astronomy dealing with "the behavior, physical properties, dynamic processes of celestial objects and phenomena."
In some cases, as in the introduction of the introductory textbook The Physical Universe by Frank Shu, "astronomy" may be used to describe the qualitative study of the subject, whereas "astrophysics" is used to describe the physics-oriented version of the subject. However, since most modern astronomical research deals with subjects related to physics, modern astronomy could be called astrophysics; some fields, such as astrometry, are purely astronomy rather than astrophysics. Various departments in which scientists carry out research on this subject may use "astronomy" and "astrophysics" depending on whether the department is affiliated with a physics department, many professional astronomers have physics rather than astronomy degrees; some titles of the leading scientific journals in this field include The Astronomical Journal, The Astrophysical Journal, Astronomy and Astrophysics. In early historic times, astronomy only consisted of the observation and predictions of the motions of objects visible to the naked eye.
In some locations, early cultures assembled massive artifacts that had some astronomical purpose. In addition to their ceremonial uses, these observatories could be employed to determine the seasons, an important factor in knowing when to plant crops and in understanding the length of the year. Before tools such as the telescope were invented, early study of the stars was conducted using the naked eye; as civilizations developed, most notably in Mesopotamia, Persia, China and Central America, astronomical observatories were assembled and ideas on the nature of the Universe began to develop. Most early astronomy consisted of mapping the positions of the stars and planets, a science now referred to as astrometry. From these observations, early ideas about the motions of the planets were formed, the nature of the Sun and the Earth in the Universe were explored philosophically; the Earth was believed to be the center of the Universe with the Sun, the Moon and the stars rotating around it. This is known as the geocentric model of the Ptolemaic system, named after Ptolemy.
A important early development was the beginning of mathematical and scientific astronomy, which began among the Babylonians, who laid the foundations for the astronomical traditions that developed in many other civilizations. The Babylonians discovered. Following the Babylonians, significant advances in astronomy were made in ancient Greece and the Hellenistic world. Greek astronomy is characterized from the start by seeking a rational, physical explanation for celestial phenomena. In the 3rd century BC, Aristarchus of Samos estimated the size and distance of the Moon and Sun, he proposed a model of the Solar System where the Earth and planets rotated around the Sun, now called the heliocentric model. In the 2nd century BC, Hipparchus discovered precession, calculated the size and distance of the Moon and inven
Calendar reform or calendrical reform, is any significant revision of a calendar system. The term sometimes is used instead for a proposal to switch to a different calendar design; the prime objective of a calendar is to unambiguously identify any day throughout history by a specific date. Periods that contain multiple days, like weeks and years, are secondary features of a calendar for convenience. Most cultures adopt a primary dating system, but different cultures have always needed to align multiple calendars with each other, because they coexisted in the same space or had established trading relations. Once specified, a calendar design cannot be altered without becoming a new one, but if a design is sufficiently close to the one used before in the local calendar system, switching to it and hence a calendar reform is possible without disruption; some design changes, will yield date identifiers different from the previous design for some days in the distant past or future. The calendar system must clarify whether dates are changed to the new design retroactively or whether the design in use and there shall be respected.
Calendar schisms happen if not all cultures that adopted a common calendar system before perform a calendar reform at the same time. If date identifiers are similar but different and mistakes are unavoidable. Most calendars have several rules which could be altered by reform: Whether and how days are grouped into subdivisions such as months and weeks, days outside those subdivisions, if any. Which years are common years and how they differ. Numbering of years, selection of the epoch, the issue of year zero. Start of the year. If a week is retained, the start and names of its days. Start of the day. If months are retained, number and names of months. Special days and periods. Alignment with social cycles. Alignment with astronomical cycles. Alignment with biological cycles. Literal notation of dates. Most calendar reforms have been made in order to synchronize the calendar with the astronomical year and/or the synodic month in lunar or lunisolar calendars. Most reforms for calendars have been to make them more accurate.
This has happened to various lunar and lunisolar calendars, the Julian calendar when it was altered to the Gregorian calendar. The fundamental problems of the calendar are that the astronomical year has neither a whole number of days nor a whole number of lunar months; such remainders could accumulate from one period to the next, thereby driving the cycles out of synch. A typical solution to force synchronization is'intercalation'; this means adding an extra day into the cycle. An alternative approach is to ignore the mismatch and let the cycles continue to drift apart; the general approaches include: The lunar calendar, which fits days into the cycle of lunar months, adding an extra day when needed, while ignoring the annual solar cycle of the seasons. The solar calendar, which fits artificial months into the year, adding an extra day into one month when needed, while ignoring the lunar cycle of new/full moons; the lunisolar calendar, which keeps both the lunar and solar cycles, adding an extra month into the year when needed.
An obvious disadvantage of the lunisolar method of inserting a whole extra month is the large irregularity of the length of the year from one to the next. The simplicity of a lunar calendar has always been outweighed by its inability to track the seasons, a solar calendar is used in conjunction to remedy this defect. Identifying the lunar cycle month requires straightforward observation of the Moon on a clear night. However, identifying seasonal cycles requires much more methodical observation of stars or a device to track solar day-to-day progression, such as that established at places like Stonehenge. After centuries of empirical observations, the theoretical aspects of calendar construction could become more refined, enabling predictions that identified the need for reform. There have been 50 to 100 reforms of the traditional Chinese calendar over 2500 years, most of which were intended to better fit the calendar months to astronomical lunations and to more add the extra month so that the regular months maintain their proper seasonal positions though each seasonal marker can occur anywhere within its month.
There have been at least four similar reforms of the lunisolar version of the Hindu calendar, all intended to make the month a better match to the lunation and to make the year a better fit to the sidereal year. There have been reforms of the solar version of the Hindu calendar which changed the distribution of the days in each month to better match the length of time that the Sun spends in each sidereal zodiacal sign; the same applies to the Buddhist calendar. The first millennium reform of the Hebrew calendar changed it from an observational calendar into a calculated calendar; the Islamic calendar was a reform of the preceding lunisolar calendar which divorced it from the solar year. Another reform was performed in Seljuk Persia by Omar Khayyam and others, developing the computed Jalali calendar; when Julius Caesar