Reform of the Calendar
For the measurement of time the most important units furnished by
natural phenomena are the Day and the Year. In regard of both, it
is convenient and usual to speak of the apparent movements of the
sun and stars as if they were real, and not occasioned by the
rotation and revolution of the earth.
The Day is the interval between two successive passages of the sun
across the meridian of any place. It is commonly computed from the
midnight passage across the inferior meridian on the opposite side
of the globe; but by astronomers from the passage at the noon
following. The Civil Day is thus twelve hours in advance of the
Astronomical.
The Solar Day, which is what we always mean by this term day, is
longer by about four minutes of time than the Sidereal, or the
successive passages of a fixed star across the same meridian; for,
owing to the revolution of the earth in its orbit from west to
east, the sun appears to travel annually in a path (the ecliptic),
likewise from west to east, among the stars round the entire
heavens. The belt of constellations through which it appears to
proceed is styled the zodiac. During half the year (March to
September) the ecliptic lies to the north of the celestial
equator; during the other half (September to March) to the south.
The points where ecliptic and equator intersect are called the
equinoxes. In the northern hemisphere the March equinox (or "first
point of Aries") is called the vernal equinox; the September
equinox ("first point of Libra"), the autumnal.
The Year (Tropical Year) is the period in which the sun makes a
complete circuit of the heavens and returns to the point in the
zodiac whence it started, and the problem to be solved by those
who construct calendars is to find the exact measure of this
yearly period in terms of days, for the number of these occupied
by the sun's annual journey is not exact. Taking the vernal
equinox as a convenient starting-point, it is found that before
the sun arrives there again, 365 days and something more have
passed. These are, of course, solar days; of sidereal days, each
shorter by four minutes, there are 366. The first attempt to find
a practical solution of this problem was made by Julius C�sar, who
introduced the Julian Calendar. With the assistance of the
astronomers of Alexandria, he determined the true length of the
year to be 365 days and 6 hours, or a quarter of a day. From this
it followed that the reckoning of the civil year began too soon,
i.e. six hours before the sun had reached the point whence it
started its annual cycle. In four years, therefore, the year would
begin an entire day too soon. To remedy this C�sar instituted
leap-years, a 366th day being introduced in every fourth year, to
cover the fractional portions of a day thus accumulated. This
extra day was assigned to February, the 24th and 25th day of which
were styled in leap-year the sixth before the calends (or first)
of March. Hence the name Bissextile given to these years.
C�sar's reform, which was introduced in the year 46 B.C., would
have been perfect had the calculation on which it was based been
accurate. In reality, however, the portion of a day to be dealt
with, over and above the complete 365, is not quite six hours, but
11 minutes and 14 seconds less. To add a day every fourth year
was, therefore, almost three quarters of an hour too much, the
following new year commencing 44 minutes and 52 seconds after the
sun had passed the equinox. At the end of a century these
accumulated errors amounted to about three-quarters of a day, and
at the end of four centuries to three entire days. The practical
inconveniences of this defect in the system were not slow in
making themselves felt, the more so as, C�sar being murdered soon
after (44 B.C.), leap-year, by a misunderstanding of his play,
occurred every third year, instead of every fourth. At the time of
the Julian reform the sun passed the vernal equinox on 25 March,
but by the time of the Council of Nic�a (A.D. 325) this had been
changed For the 21st, which was then fixed upon as the proper date
of the equinox--a date of great importance for the calculation of
Easter, and therefore of all the moveable feasts throughout the
year.
But the error, of course, continued to operate and disturb such
arrangements. In the thirteenth century the year was seven days
behind the Nic�an computation. By the sixteenth it was ten days in
arrear, so that the vernal equinox fell on 11 March, and the
autumnal on 11 September; the shortest day was 11 December, and
the longest 11 June, the feast of St. Barnabas, whence-the old
rhyme:
Barnaby bright, the longest day and the shortest night.
Such alterations were too obvious to be ignored, and throughout
the Middle Ages many observers both pointed them out and
endeavoured to devise a remedy. For this purpose it was necessary,
however, not only to determine with accuracy the exact amount of
the Julian error, but also to discover a practical means of
correcting it. It was this latter problem that chiefly stood in
the way of reform, for the amount of error was ascertained almost
exactly as early as the thirteenth century. The necessity of a
reform was continually urged, especially by Church authorities,
who felt the need in connexion with the ecclesiastical calendar.
It was accordingly strongly pressed upon the attention of the pope
by the councils of Constance, Basle, Lateran (A.D. 1511), and
finally by Trent, in its last session (A.D. 1563).
Nineteen years later the work was accomplished by Pope Gregory
XIII (from whom the Gregorian reform takes its name) with the aid
chiefly of Lilius, Clavius, and Chacon or Chaconius. There were
two main objects to be attained: first, the error of ten days,
already mentioned, which had crept in, had to be got rid of;
second, its recurrence had to be prevented for the future. The
first was attained by the omission from the calendar of the ten
superfluous days, so as to bring things back to their proper
position. To obviate the recurrence of the same convenience, it
was decided to omit three leap years in every four centuries, and
thus eliminate the three superfluous days, which, as we have seen,
would be introduced in that period under the Julian system. To
effect this, only those Centurial years were retained as leap
years the first two figures of which are exact multiples of 4--as
1600, 2000, 2400--other centurial years 1700, 1800, 1900, 2100,
etc.--becoming common years of 365 days each. By this
comparatively simple device an approximation to perfect accuracy
was effected, which for all practical purposes is amply
sufficient; for, although the length of the Gregorian year exceeds
the true astronomical measurement by twenty-six seconds, it will
be about thirty-five centuries before the result will be an error
of a day, and, as Lord Grimthorpe truly says, before that time
arrives mankind will have abundant time to devise a mode of
correction. For the actual introduction of the Gregorian Calendar
or New Style, throughout Christendom, see CHRONOLOGY.
JOHN GERARD
Transcribed by Rick McCarty
http://www.knight.org/advent
From the Catholic Encyclopedia, copyright � 1913 by the
Encyclopedia Press, Inc. Electronic version copyright � 1996 by
New Advent, Inc.
Taken from the New Advent Web Page (www.knight.org/advent).
This article is part of the Catholic Encyclopedia Project, an
effort aimed at placing the entire Catholic Encyclopedia 1913
edition on the World Wide Web. The coordinator is Kevin Knight,
editor of the New Advent Catholic Website. If you would like to
contribute to this worthwhile project, you can contact him by e-
mail at (knight.org/advent). For more information please download
the file cathen.txt/.zip.
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