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Astro*Dictionary by Michael Erlewine





4 articles for "Calendar"

Calendar [Astro*Index]

A system of reckoning time over extended intervals by combining days into various periods adapted to purposes of civil life, fixing religious observances, or meeting scientific needs. Three of the periods used in calendars (days, months, and years) are based on astronomical periods that are of importance for the practical activities of daily life. Others, such as the week, are artificial.

Calendarial reckoning follows conventional calendar years and adopted historical eras. In constructing and regulating civil calendars, and fixing ecclesiastical calendars, a number of auxiliary cycles and periods are used. The principal chronological eras and cycles (with the equivalent dates in the Gregorian calendar, when appropriate) are listed in the Astronomical Ephemeris, which includes the following entries: Chronological Cycles: Dominical Letter, Epact, Golden Number (Lunar Cycle), Julian Period (year of), Roman Indiction, and Solar Cycle, together with the Julian Day Number corresponding to January 1 of the given year, and the conversion from Julian calendar to Gregorian calendar for a selected date of the given year; ERAS: Byzantine, Jewish (A.M.), Roman (A.U.C.), Nabonassar, Japanese, Grecian (Seleucidae), Indian (Saka), Diocletian, Mohammedan (Hegira); Religious Calendars: Epiphany, Septuagesima Sunday, Quinquagesima (Shrove) Sunday, Ash Wednesday, Palm Sunday, Good Friday, Easter Day, Rogation Sunday, Ascension Day (Holy Thursday, Whit Sunday), Pentecost, Trinity Sunday, Corpus Christi, First Sunday in Advent, Christmas Day, First day of Passover (Pesach), Feast of Weeks (Shebuoth), Jewish New Year (tabular) (Rosh Hashanah), Day of Atonement (Yom Kippur), First day of Tabernacles (Succoth), Mohammedan New Year (tabular), First day of Ramadan (tabular).

The complexity of calendars is due mainly to the incommensurability of the astronomical periods on which they are based. The supply of light by the Sun and Moon is governed by the solar day and the synodic month, while the return of the seasons depends on the tropical year. For the epoch 1900.0, the length of the synodic month is 29.530589 days, and of the tropical year 365.242199 days; the very small and somewhat uncertain secular variations in the lengths of these periods are unimportant for chronological purposes. At the epoch 1900.0, there are 12.368267 lunations in a tropical year. The many calendars of historical times were primarily lunar in origin, the year consisting usually of 12 months of about 30 days, with arbitrary or calculated intercalation of months or days to make the length of the year conform to the solar year. One of the Egyptian calendars was, up to the time of Julius Caesar's reform of the Roman calendar in 46 BC, the only civil calendar in which the length of each month and year was fixed by rule rather than determined by the discretion of officials or by direct observation of some astronomical event. See also: - Babylonian Calendar - Chinese Calendar - Ecclesiastical Calendar - Egyptian Calendar - Greek Calendar - Gregorian Calendar - Hebrew Calendar - Hindu Calendar - Horakti Calendar - Julian Calendar - Moslem Calendar - Sothic Calendar

See also:
♦ Babylonian Calendar ♦ Astronomical ♦ Chinese Calendar ♦ Ecclesiastical Calendar ♦ Egyptian Calendar ♦ Greek Calendar ♦ Gregorian Calendar ♦ Hebrew Calendar ♦ Hindu Calendar ♦ Horakti Calendar ♦ Julian Calendar ♦ Moslem Calendar ♦ Sothic Calendar
Calendar [DeVore]

A system of reckoning and recording the time when events occur; the coordination of the days, weeks, and months of the year with the cycles upon which they are based.

The frequency with which astrologers have been known to accept without question a birthdate that a little inquiry would reveal as a Julian date, rather suggests that sometimes we strain at a gnat and swallow a camel: calculating with great care to the hour and minute, cusps and planets' places for a date that is 10 or 11 days in error according to the calendar on which our computations are based.

Throughout the centuries the recording of time has been a problem, to the study of which lifetimes have been devoted. To the historian the correct day is important, but to the astrologer the correct hour of the correct day is not only important — it is essential. An aftermath of World War II will probably be an increasing number of contacts with people who have Julian birthdates, and who know so little about astrology that the importance of reimpressing their birthdate upon their memory in Gregorian terms never occurs to them.

To render more vivid the problem of the world's calendar makers, there is presented a survey of the manner in which it has been met in different epochs and in remote countries. Fundamentally time is reckoned by the Earth's rotation on its axis with reference to the Sun, a day; by the Moon's revolution around the Earth, a month; and by the Earth's revolution around the Sun, a year. Of mechanical gadgets for recording the passing of time, their number is legion; but their correction always comes from the astronomical observatory.

The recurrence of the Vernal Equinox on the same day each year is the one supreme and inflexible necessity — and that we have not even yet fully attained. In astrology, the complexities arising out of a variety of calendars constitute a major problem. The day is universal as a unit of time, but to group days into months, and months into a year, and keep in step with the universe and the seasons introduces serious difficulties. Days do not add up to lunar months, and months do not add up to years, other than through recourse to numerous devices and ingenious compromises. The planets pursue their inexorable courses, wholly unmindful of man's need for a method whereby to determine the places they occupied at a given moment of time. The moment is easy enough to identify when it occurs, but how to record the moment in terminology that will suffice to identify it a century later is a vastly more difficult problem. A study of the various calendars is perhaps the shortest way to an appreciation of the importance of a matter which involves the basic facts with which the astrologer must deal.

The Mohammedan calendar is one of the most primitive. It is strictly a Lunar calendar, the year consisting of twelve lunar months, which retrograde through the seasons in about 32½years. To reconcile the lunar cycle to a given number of complete days, a leap year is introduced on the 2nd, 5th, 7th, 10th, 13th, 16th, 18th, 21st, 24th, 26th and 29th years of a thirty year cycle, making these years consist of 355 days instead of 354.

The names of the months and the number of days are:

1, Muharram (30); 2, Saphar (29); 3, Rabia I (30); 4, Rabia II (29); 5, Jomada I (30); 6, Jomada II (29); 7, Rajah (30); 8, Shaaban (29); 9, Ramadan (30); 10, Shawaal (29); 11, Dulkasda (30); and 12, Dulheggia (29 or 30). The years are calculated from July 16, 622 A.D., the day following the Hegira, the flight of Mohammed from Mecca to Medina after an attempted assassination. The beginning of the 46th cycle, with the first day of Muharram, in the year 1351, compares to May 7, 1932 of the Gregorian calendar; continuing:

		1365   Dec. 6, 1945
		1366   Nov. 25, 1946
		1367   Nov. 15, 1947
		1368   Nov. 3, 1948
		1369   Oct. 24, 1949
		1370   Oct. 13, 1950
		1371   Oct. 2, 1951
		1372   Sept. 21, 1952
		1373   Sept. 10, 1953
		1374   Aug. 30, 1954

To find the Gregorian equivalent to any Mohammedan date multiply 970,224 by the Mohammedan year, point off six decimal places and add 621.5774. The whole number will be the year A.D., and the decimal multiplied by 365 will be the day of the year.

The Egyptian calendar divided the year into twelve months of 30 days each, with five supplemental days following each twelfth month. Because it ignored the quarter day annual loss, it likewise retrograded through the seasons in 1460 years, hence 1461 Egyptian years are equal to 1460 Julian years. The Egyptian year has been called vague, because at different epochs it has commenced at different seasons of the year.

The inadequacy of these calendars, because totally unrelated to the cycle of the seasons, is obvious. The Hindu calendar of India is one of the early lunisolar calendars, wherein the year is divided into twelve months, with an intercalated month bearing the same name, inserted after every month in which there are two lunations, which is about every three years. The year commences about April 11, and is divided into the following months: Baisakh, Jeth, Asarh, Sarawan, Bhadon, Asin or Kuar, Kartik, Aghan, Pus, Magh, Phalgun, and Chait.

Another lunisolar compromise is the Chinese calendar, wherein the year begins with the first new Moon after the Sun enters Aquarius. It consists of 12 months, with an intercalary month every 30 months, each month divided into thirds. It dates from 2697 B.C., whereby the Gregorian equivalent of the Chinese year 4647 is 1950 A.D.


The Jewish calendar is likewise a lunisolar calendar, which reckons from 3761 B.C., the traditional year of the Creation. The ecclesiastical year begins with the first New Moon after the Vernal Equinox, but the civil year begins with the new Moon following the Autumnal Equinox. The years are either defective' of 353 d., regular, of 354 d. or perfect, of 355 d., with an intercalated month on the 3rd, 6th, 8th, 11th, 14th, 17th and 19th years of the 19-year Metonic cycle. Each month begins on the new moon — not the moment of the Lunation but of the new moon's visibility — allowing some elasticity for bringing certain Festivals on suitable days of the week. The Jewish civil calendar, and its important days, runs thus:

  1. The so-called October new Moon. Tishri (30 d.). New Year's day, or Rosh Hashanah; containing the Feast of Gedelis; Yom- kippur; Succoth, Hashana Rabba; Shemini-Atzereth; and Simchath- Torah.
  2. Heshvan (29 or 30 d.).
  3. Kislev (29 or 30 d.) containing Hanaca.
  4. Teveth (29 d.); containing the Fast of Teveth.
  5. Shevat (30 d.).
  6. Adar (29 d. or 30 d.). Ve-Adar (29 d.). An intercalary month on leap years, containing the Fast of Esther, and Purim.
  7. Iyar (29 d.); containing Lag B'omer.
  8. Sivan (30 d.); containing Shevuoth.
  9. Tamuz (29 d.); containing the Fast of Tamuz, for the taking of Jerusalem.
  10. Av (30 d.) ; containing the Fast of Av, for the Destruction of the Temple.
  11. Ellul (29 d.).

The current Lunar cycle, the 301st, consists of these comparative years:

		5701   Oct. 3, 1940
		5702   Sept. 22, 1941
		5703   Sept. 12, 1942
		5704   Sept. 30, 1943
		5705   Sept. 18, 1944
		5706   Sept. 8, 1945
		5707   Sept. 26, 1946
		5708   Sept. 15, 1947
		5709   Oct. 4, 1948
		571O   Sept. 24, 1949
		5711   Sept. 12, 1950
		5712   Oct. 1, 1951
		5713   Sept. 20, 1952
		5714   Sept. 1O, 1953
		5715   Sept. 28, 1954
		5716   Sept. 17, 1955
		5717   Sept. 6, 1956
		5718   Sept. 26, 1957
		5719   Sept. 15, 1958

The Roman calendar is presumed originally to have consisted of ten months, of a total of 304 days, beginning with Martius and ending with December. Numa added January and February, bringing it up to 355 d., and ordered an intercalary month every second year. The Romans counted backwards from three fixed points in the month: the calends, the 1st; the ides, the 15th of March, May, July and October, and the 13th of other months; and the nones, the 8th day before the ides. Thus the ides of March was March 15th; March 13th was the third day before the ides; March 7th was the nones of March; while March 30th was the third day before the calends of April. Abuse of power by the pontiffs and the many wars of conquest prior to the Christian era finally so disrupted the Roman calendar that after his conquest of Egypt Julius Caesar brought to Rome a Greek astronomer, Sosigines, who with the aid of Marcus Fabius accomplished the first great calendar reform, the Julian calendar, named after himself, which went into effect through the civilized world in 45 B.C., and continued in use until 1582 A.D. These reforms consisted of the following:

(1) The equinox was returned to March, by inserting two months between November and December of 46 B.C., creating what was thereafter known as "the last year of confusion."
(2) The lunar year and the intercalary month were abolished.
(3) The length of the mean solar year was fixed at 365.25 days, the length at which the ancients had figured it.
(4) To compensate for the accumulation of these fractions into a day every four years, the extra day was inserted at the end of February, then the last month of the year, making it a "leap year" of 366 days.
(5) Renamed Quintilis, the fifth month, after himself, calling it Juli.
(6) Evenly distributed the days among the months, 30 days to the even months, and 31 days to the odd months, except February which had 30 days only in leap year.
(7) Ordered it to take effect January 1, 45 B.C.
However, despite the fact that the Julian calendar went into effect on January 1st, the civil year continued to date from March 25th.

The system was slightly disarranged by Augustus, who renamed Sextilis as August, but refusing to be honored by a shorter month than Julius, ordered it increased to 31 days, reducing February to 28 days except on leap years. Hence, to him we owe the irregular arrangement of the 30 and 3i day months, and the poem we moderns must recite in order to tell which are which. He did, however, render one important service, not without its droll aspects, by suspending leap years for some eleven years to correct a 3-day error which had progressively accumulated because the pontiffs had been intercalating every third instead of every fourth year for some 36 years, and this error of from 1 to 3 days in the chronology of the period has never been corrected.

Meanwhile the Equinox continued to retrograde. When Julius introduced his reform it fell on March 25th; by 325, the Council at Nicea, it was the 21st; by 1570 it was the 11th. The Venerable Bede had called attention to it in the 8th Century and John Holywood in the 13th. Roger Bacon finally wrote a thesis on calendar reform and sent it to the Pope; and in 1474 Pope Sixtus IV summoned Regiomontanus to Rome to superintend a reconstruction of the calendar, but he died with the task unfinished.

A century later Aloysius Lilius, a Verona physician and astronomer and doubtless an astrologer, worked out what he believed to be the exact requirements for a calendar that would keep step with the seasons. After his death his brother presented the plan to Pope Gregory XII, who gathered a group of learned men to discuss it, including Clavius, who later wrote an 800-page Treatise explaining it. Thus it was that after five years of study the Gregorian calendar was put into effect in 1582, instituting the following reforms:

(1) Ten days were dropped by ordering October 5th to be counted as October 15th.
(2) The length of the solar year was corrected to 365 d. 5 h. 49 m. 12 s.
(3) The year was made to begin January 1.
(4) The centesimal years were made leap years only if divisible by 400 — thereby gaining the fraction of a day per hundred years that in fifteen centuries had amounted to ten days.

The new calendar was immediately adopted in all Roman Catholic countries, but the rest of the world was slow to accept it. Germany, Denmark and Sweden did not adopt it until 1700.

In Anglo-Saxon England the year began December 25th, until William of Normandy, following his conquest of England, ordered it to begin on January 1st, chiefly because this was the day of his coronation. Later England adopted March 25th, to coincide with the date on which most of the Christian peoples of the medieval epoch reckoned the beginning of the year. By edict Constantine later made Easter the beginning of the year, and it continued to be observed as New Year's Day until 1565, when Charles IV changed it back to January 1st.

Not until 1752 did Britain finally adopt the Gregorian calendar, suppressing 11 days and ordering that the day following September 2, 1752 be accounted as September 14th. Those who objected to the disruption of the week of festivities with which they were wont to celebrate the New Year, March 25th to April 1st, were sent mock gifts, or paid pretendedly ceremonious calls on April 1st, a custom that survives today in April Fool's Day.

The countries under the sway of the Greek orthodox church continued to follow the Julian calendar, and not until 1918 did Russia finally adopt it. Those to whom the calendar is an economic necessity, and who are proposing various calendar reforms designed to facilitate interest computations and achieve uniformity of holidays, find themselves impeded by the requirements of the Ecclesiastical Calendar as set forth by the Council of Nicea, 325 A.D., as follows:

(1) Easter must fall on a Sunday;
(2) This Sunday must follow the 14th day after the Paschal Moon;
(3) The Paschal Moon is that Full Moon of which the Lunation 14 days thereafter falls on or next after the day of the Vernal Equinox;
(4) The Vernal Equinox is fixed in the calendar as the 21st of March.

It was then provided that if the 14th day after the Paschal Moon falls on a Sunday, the following Sunday is to be celebrated as Easter — to make certain that it did not coincide with the Jewish Passover. Thereby did history again repeat itself, for according to Dio Cassius the Egyptians began the week on Saturday, but the Jews, from hatred of their ancient oppressors, made it the last day of the week.

To make Easter a fixed date in the calendar, such as April 8th, the suggestion of which has been advanced, would not only disturb the ecclesiastical calendar, but most of the proposed plans would destroy the continuity of the days of the week and upset the system of planetary hour rulerships which is almost as ancient as the recording of time. The seven days of the week represented the quadrants of the Moon's period in an age when time was reckoned almost entirely by the Moon. Methuselah's great age of 969 years was doubtless that many lunar months, then called years, which if reduced to Gregorian years as we know them would make him around 79 years of age.

The all but universal division of the year into twelve months, and of the Earth's annual orbit into twelve arcs, appears to be a recognition of the changes in equilibrium that take place during the traversal of the circuit: a moving body (the Earth) bent into an orbit, by the attraction of a gravitational center (the Sun) which also pursues an orbit around a more remote gravitational center (the center of our Milky Way galaxy). Present astronomical opinion places this center at a remote point in the direction of 0° Capricorn, which is also the direction of the Earth's polar inclination. This suggests that it may not be merely the Earth that oscillates, causing the pole to describe the circle from which results the 25,000-year precessional cycle, but the entire plane of the Earth's motion. This would be analogous to the Moon's intersection of the plane of the Earth's orbit at the Nodes, at an inclination of 5°, thereby producing a three-dimensional motion. The Earth's orbit may even be inclined to the Sun by the amount of the polar inclination making the equinoctial points the Earth's nodes of intersection with the plane of the Sun's orbit. In any event in order that the calendar shall coincide with the seasons it must bear a fixed relationship to the Vernal Equinox, for in the last analysis the unit by which the year is determined is the Earth's orbit as measured from one Vernal Equinox to the next. The few moments of time represented by the discrepancy between a complete circle and the precession of the point of reference is the only figment of time actually thrown away and unaccounted for in any calendar.

If we must have calendar reform, it would be far more practical to make the year begin at the Vernal Equinox, and so allocate the days among the months that the first day of each successive month shall coincide approximately with the ingress of the Sun into each sign. This could be accomplished by 12 months of 30 days each, with a 31st day after the 2nd, 4th, 6th, 8th and 10th months, and on leap years after the 12th month; and by making all the 31st days holidays or moratorium days, hence not to be included in any calculations of interest, rent or other legal considerations. The legal year would consist 360 days, and computations be thereby greatly simplified.

If some one February were ordered prolonged by 20 days, February 48th to be followed by March 1st on the day of the Vernal Equinox, it would reinstate September to December as respectively the 7th, 8th, 9th, and 10th months, and end the year with FebruarY 30th, or on leap years, the 3st. The holidays could readily be celebrated on these moratorium days, and even the Fourth of July could preserve its name and character and still be observed on the moratorium day that preceded the first day of July.

There would be no advantage in making Easter a fixed date, and its determination under present rules could still be done as readily as is the date for the Jewish Passover. Such a reform would, however, result in great psychological gain to the peoples of the world. Some claim, on Biblical authority, that the year should begin on the Summer Solstice, and that by dedicating to the Creator the middle of the 3 days when the Sun hangs motionless, the year will divide into 2 halves of equal size, each consisting of 182 days — the first half feminine and the second half masculine.

The importance of a New Year point of beginning is to be seen in the manner in which in all ages the advent of the New Year has been celebrated with festivities.

Babylon, in 2250 B.C., celebrated New Year at the Vernal Equinox, with an 11-day festival, Zagmuk, in honor of their patron deity, Marduk. The Egyptians, Phoenicians and Persians celebrated it at the time of the Autumnal Equinox. Until the fifth century B.C., the Greeks celebrated it at the Winter Solstice, as did the Romans with a festival dedicated to Saturn — the Saturnalia. To counteract this revelry the early Christians celebrated it in commemoration of the birth of Jesus with prayer and acts of charity. When the year was made to begin on January 1st, Christmas was shifted to December 25th, the octave of New Year's day, the while Pagan Rome made sacrifices to Janus, after whom January was named. Janus, guardian deity of gates, was represented with two faces, watching both entering and departing wayfarers: the going out of the old year and the coming in of the new.

Emperors began extorting tribute (strena) by way of New Year's gifts. Henry III of England followed this precedent, a custom which did not become entirely obsolete until the Commonwealth.

The Scottish name for New Year's Eve is Hogmany, when the children ran around singing and begging gifts in the form of oaten cakes. The Parsees, Persians who emigrated to India, celebrate Yazdegera with worship of their divinities and visits to their friends to join hands in the ceremony of hamijar. The Druids distributed sprigs of sacred misletoe. On the continent the New Year giving of strenae "for luck" still survives, but in English-speaking countries it has been superseded by the Christmas gift, while the wassail-bowl has now become a bowl of eggnog.


To harmonize dates in the Gregorian calendar with the degrees of the Zodiac the accompanying table "The Calendar in the Zodiac" has been compiled by averaging the Sun positions of the different degrees with the days of the month over a period of a century.


For correlating the correct day of the week with the first day of the month in different years, use is made of the Dominical letter — literally the Sunday letter. From Table 1, find the Dominical letter for the required year; then from Table 11 determine which of the monthly calendars — numbered 1 to 7 — is applicable to the date under consideration. These tables will supply the day of the week of any date in the Gregorian calendar, forever. Take only the first two digits of the year and divide by 4. If the remainder is 1, use column 1 of Table I: similarly with columns 2 and 3: or if no remainder, use the last column, marked 0. Bissextile years have two Dominical letters: the first for January and February, and the other for the remainder of the year.

To find the Dominical letter of any date in the Julian calendar (45 B.C. to 1582 A.D.) add 9 to the year, and divide by 28. The quotient is the number of 28-year cycles that have elapsed, but the remainder is the year of the cycle. If there is no remainder it is, of course, the last year of the cycle.

In using the remainder, bear in mind that the first year of the Christian era, the tenth of that cycle, began on Saturday, hence the Dominical letter was B. The next year it was A; then G. For 4 A.D., a bissextile year, it was F in January and February, and E for the balance of the year. For 5 A.D. it was D — and so on, as in column 1, Table I.

See also:
♦ Babylonian Calendar ♦ Astronomical ♦ Chinese Calendar ♦ Ecclesiastical Calendar ♦ Egyptian Calendar ♦ Greek Calendar ♦ Gregorian Calendar ♦ Hebrew Calendar ♦ Hindu Calendar ♦ Horakti Calendar ♦ Julian Calendar ♦ Moslem Calendar ♦ Sothic Calendar
Calendar Month [Astro*Index]

The normal calendar months, January, February, March, etc; a convenient division of the year based upon solar or lunar cycles with respect to the fixed stars.

See also: ♦ Fixed Star
Calendar Year [Astro*Index]

The civil year, or year used for the modern (Gregorian) calendar, consisting of 365 days with an extra day added every fourth or leap year but omitted in century years not evenly divisible by 400.

See also: ♦ Gregorian Calendar ♦ Julian Calendar


Astro*Index Copyright © 1997 Michael Erlewine


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