The Encyclopedia Americana (1920)/Calendar
CALENDAR, a system of dividing time
into years, months, weeks and days for use in
civil life, or a register of these or similar
divisions. Among the old Romans, for want of
such a register, it was the custom of the
pontifex maximus, on the first day of the
month, which began with the new moon, to
proclaim (calare) the month, with the festivals
occurring in it. Hence, calendæ (the first of
the month) and calendar. The periodical
occurrence of certain natural phenomena gave rise
to the first division of time. The apparent daily
revolution of the sun about the earth occasioned
the division into days. The time at which a day
begins and ends has been differently fixed, the
reckoning being from sunrise to sunrise, from
sunset to sunset, from noon to noon, or from
midnight to midnight. The changes of the
moon, which were observed to recur every 29
or 30 days, suggested the division into months,
but the month now used, though nearly equal
to a lunation, is really an arbitrary unit; and,
as a still longer measure of time was found
necessary for many purposes, it was supplied
by the apparent yearly revolution of the sun
round the earth, producing the changing seasons.
The time of this revolution is now known
to be 365 days, 5 hours, 48 minutes and 46
seconds, but as it has at various times been
reckoned differently, this has given rise to
corresponding changes in the calendar. This unit
of time is called a solar year. The division

into weeks, which has been almost universally
adopted, is not founded on any natural
phenomenon, and, as it originated in the East, has
been attributed to the divine command to
Moses in regard to the observation of the
seventh day as a day of rest. By other authorities
it has been ascribed to the number of the
principal planets, a theory supported by the
names given to the days. It was not used by
the Greeks, nor by the Romans, till the time of
Theodosius. The great influence of the sun's
course upon the seasons naturally attracted the
attention of men at all periods to this
phenomenon; accordingly all nations in any
degree civilized have adopted the year as the
longest unit of time. The year of the ancient
Egyptians was based on the changes of the
seasons alone, without reference to the lunar
month, and contained 365 days, which were
divided into 12 months of 30 days each, with
five supplementary days at the end of each
year. The Jewish year consisted of lunar
months, of which they reckoned 12 in the year,
intercalating a 13th when necessary to maintain
the correspondence of the particular
months with the regular recurrence of the
seasons. The Greeks in the earliest period
also reckoned by lunar and intercalary months.
They divided the month into three decades, a
system also adopted long afterward at the time
of the French Revolution. It possesses the
advantage of making the smaller division an exact
measure of the larger, and under it the number
of a day in the 10-day period readily
suggests its number in the month. The Greeks
in the time of Solon had a year of 12 months
alternately of 29 and 30 days, the total number
of days being 354, and the year being very
nearly equal to a lunar one. Soon afterward a
month of 30 days began to be intercalated every
other year in order to reconcile their year with
that founded on the sun's movement, but as the
error was still very large the intercalary month
was afterward omitted once in four times. The
Jewish and also the Greek year thus both
varied in duration according as the intercalary
month was introduced or omitted. This, with
the uncertainty as to the exact duration of the
year, was a constant source of confusion.

Various plans for the reformation of the
calendar were proposed from time to time; but
all proved insufficient till Meton and Euctemon
finally succeeded in bringing it to a much
greater degree of accuracy by fixing on the
period of 19 years, in which time the new
moons return upon the same days of the year
as before (as 19 solar years are very nearly
equal to 235 lunations). (See ). This
mode of computation, first adopted by the
Greeks about 432 B.C., was so much approved
of that it was engraven with golden letters on
a tablet at Athens. Hence the number showing
what year of the moon's cycle any given year
is is called the golden number. This period of
19 years was found, however, to be about six
hours too long. This defect Calippus, about
102 years later, endeavored to remedy, but still
failed to make the beginning of the seasons
return on the same fixed day of the year.

The Romans first divided the year into 10
months, but they early adopted the Greek
method of lunar and intercalary months, making
the lunar year consist of 354, and
afterward
of 355 days, leaving 10 or 11 days and
a fraction to be supplied by the intercalary
division. This arrangement, which was placed
under the charge of the pontiffs, continued until
the time of Cæsar. The first day of the month
was called the calends. In March, May, July
and October, the 15th, in other months the 13th,
was called the ides. The ninth day before the
ides (reckoning inclusive) was called the nones.
The other days of the months they reckoned
forward to the next calends, nones, or ides,
whether in the same or the succeeding month,
always including both days in the reckoning.
Thus the 3d of March, according to the Roman
reckoning would be the fifth day before the
nones, which in that month fell on the 7th.
The 8th of January, in which month the nones
happen on the 5th, and the ides on the 13th
was called the 6th before the ides of January.
Finally to express any of the days after the
ides, they reckoned in a similar manner from
the calends of the following month. From the
inaccuracy of the Roman method of reckoning
it appears that in Cicero's time the calendar
brought the vernal equinox almost two months
later than it ought to be. To check this irregularity
Julius Cæsar invited the Greek astronomer
Sosigenes to Rome, who, with the assistance
of Marcus Fabius, invented that mode of
reckoning which, after him who introduced it
into use, has been called the Julian calendar.
The chief improvement consisted in restoring
the equinox to its proper place in March. For
this purpose two months were inserted between
November and December, so that the year 707
(46 B.C.), called from this circumstance the
year of confusion, contained 14 months. In
the number of days the Greek computation was
adopted, which made it 365¼. The number
and names of the months were kept unaltered
with the exception of Quintilis, which was
henceforth called, in honor of the author of the
improvement, Julius. To dispose of the quarter
of a day it was determined to intercalate a day
every fourth year between the 23d and 24th
of February. This was called an intercalary
day, and the year in which it took place was
called an intercalary year, or, as we term it, a
leap year.

This calendar continued in use among the
Romans until the fall of the empire, and
throughout Christendom till 1582. The festivals
of the Christian Church were determined by it.
With regard to Easter, however, it was necessary
to have reference to the course of the
moon. The Jews celebrated Easter (that is,
the Passover) on the 14th of the month Nisan
(or March); the Christians in the same month,
but always on a Sunday. Now, as the Easter
of the Christians sometimes coincided with the
Passover of the Jews, and it was thought
unchristian to celebrate so important a festival
at the same time as the Jews did, it was
resolved at the Council of Nice, 325 A.D., that
from that time Easter should be solemnized on
the Sunday following the first full moon after
the vernal equinox, which was then supposed
to take place on 21 March. As the course of
the moon was thus made the foundation for
determining the time of Easter, the lunar Cycle
of Meton whs taken for this purpose; according
to which the year contains 365¼ days, and
the new moons, after a period of 19 years,
return on the same day as before. The
inaccuracy
of this combination of the Julian year
and the lunar cycle must have soon discovered
itself on a comparison with the true time of the
commencement of the equinoxes, since the
received length of 365¼ days exceeds the true by
about 11 minutes; so that for every such Julian
year the equinox receded 11 minutes, or a day
in about 130 years. In consequence of this,
in the 16th century, the vernal equinox had
changed its place in the calendar from the 21st
to the 10th; that is, it really took place on the
10th instead of the 21st, on which it was placed
in the calendar. Luigi Lilio Ghiraldi,
frequently called Aloysius Lilius, a physician of
Verona, projected a plan for amending the
calendar, which, after his death, was presented
by his brother to Pope Gregory XIII. To
carry it into execution, the Pope assembled a
number of prelates and learned men. In 1577
the proposed change was adopted by all the
Catholic princes; and in 1582 Gregory issued a
brief abolishing the Julian calendar in all
Catholic countries, and introducing in its stead
the one now in use, under the name of the
Gregorian or reformed calendar, or the new
style, as the other was now called the old style.
The amendment ordered was this: 10 days were
to be dropped after 4 Oct 1582, and the 15th
was reckoned immediately after the 4th. Every
100th year, which by the old style was a leap
year, was now to be a common year, the 4th
century divisible by four excepted; that is, 1600
was to remain a leap year, but 1700, 1800, 1900
of the common length, and 2000 a leap year
again. In this calendar the length of the solar
year is taken to be 365 days, 5 hours, 49
minutes and 12 seconds, the difference between
which and the true length is immaterial. In
Spain, Portugal and the greater part of Italy
the amendment was introduced according to
the Pope's instructions. In France the 10 days
were dropped in December, the 10th being
called the 20th. In Catholic Switzerland,
Germany and the Netherlands the change was
introduced in the following year, in Poland in
1586, in Hungary 1587. Protestant Germany,
Holland and Denmark accepted it in 1700, and
Switzerland in 1701, In the German empire a
difference still remained for a considerable
time as to the period for observing Easter. In
England the Gregorian calendar was adopted
in 1752, in accordance with an act of Parliament
passed the previous year, the day after
2d September becoming the 14th, Sweden
followed in 1753. Russia and Greece still adhere
to the Julian calendar, which, by the interjection
of two more days, 1800 and 1900 being
regarded as leap years, now differs from the
Gregorian calendar by 13 days. Thus 14 Jan.
1917 of the new style will be 1 Jan. 1917 in
Greece and Russia.

The change adopted in the English calendar
in 1752 embraced another point. There had
been previous to this time various periods fixed
for the commencement of the year in various
countries of Europe. In France, from the time
of Charles IX, the year was reckoned to begin
from 1 January; this was also the popular
reckoning in England, but the legal and
ecclesiastical year began on 25 March. The 1st
of January was now adopted as the beginning
of the legal year, and it was customary for
some time to give two dates for the period
intervening between 1 January and 25 March,

that of the old and that of the new year, as
January 1752-53.

In France, during the Revolutionary epoch,
a new calendar was introduced by a decree of
the National Convention, 24 Nov. 1793. The
new reckoning was to begin with 22 Sept 1792,
the day on which the first decree of the new
republic had been promulgated. The year was
made to consist of 12 months of 30 days each,
and, to complete the full number, five fête days
(in leap year six) were added at the end of
the year. Instead of weeks, each month was
divided into three parts, called decades,
consisting of 10 days each; the other divisions
being also accommodated to the decimal system.
This calendar was abolished at the command of
Napoleon, by a decree of the Senate, 9 Sept.
1805, and the common or Gregorian calendar
was re-established on 1 January of the following
year. The Mohammedans employ a lunar
year of 354 days and 12 lunar months, which
have alternately 29 and 30 days. Thirty years
form a cycle and 11 times in every cycle an
extra day is added at the end of the year. The
months and the seasons do not correspond and
the first of the year may fall at any time during
the solar year.  The months are named
Muharram, Saphar, Rabia I, Rabia II, Jomadi
I, Jomadi II, Rajah, Shaaban, Ramadan,
Shawall, Dulkaada and Dulkeggia. The Mohammedan
era is computed from the first day of
the year of the Hejira, or flight of Mohammed
to Medina. It corresponds with 15 July 622
of the Christian era. The Mohammedan year
which began on 28 Oct. 1916 was the 15th year
of the 45th cycle, or the year 1335 of the
Mohammedan era. See also ;
;
; .

Bibliography. — Boll, ‘Griechisches Kalendar’
(Heidelberg 1910); Bowditch, ‘Numeration,
Calendar Systems and Astronomical
Knowledge of the Mayas’ (Cambridge, Mass.,
1910); Burnaby, ‘Elements of the Jewish and
Mohammedan Calendar’ (London 1901);
Langdon, ‘Tablets from the Archives of
Drehem, with a Complete Account of the
Origin of the Sumerian Calendar’ (Paris
1911); Mahler, ‘Etudes sur le calendrier
égyptien’ (ib. 1907); Plunket, ‘Ancient Calendars
and Constellations’ (London 1903);
Schram, ‘Kalendariographische und chronologische
Tafeln’ (Leipzig 1908).