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Astro*Dictionary by Michael Erlewine





2 articles for "Leap Year"

Leap Year [Astro*Index]

The 366-day year which occurs every fourth calendar year. To keep the year in line with the seasons, we add a full day every four years (years divisible by four: l904, l908, etc.) making the month of February 29, instead of 28, days long; this 366-day year is called a leap year. This rule would produce a calendar in which the length of the year was 365.25 days, which is a bit too large. The Gregorian Calendar (our current calendar) amends this rule as follows: Years ending in 00, such as 1800, 1900 etc., are not leap years unless the first two digits are also divisible by four. Thus, 1900 was not a leap year, but 2000 will be.

Alternative: Years in which an extra day is added to February, giving it 29 instead of 28 days. In the Julian Calendar, this was done for all years evenly divisible by 4. but, in the modern (Gregorian) calendar this rule is modified to exclude century years which are not evenly divisible by 400. This rule corrects the calendar, keeping it in close match with the seasons. Thus AD1600 and 2000 are leap years, but 1700, 1800, and 1900 were not.

See also:
♦ Year ♦ Calendar ♦ Gregorian Calendar ♦ Julian Calendar ♦ Hebrew Calendar
Leap Year [DeVore]

To preserve the coincidence of the vernal equinox in approximately correct relation to the Civil year, Caesar, with the assistance of Sosigines, introduced the Julian calendar about 46 B.C. It called for the intercalation of a day on certain years. The "last year of confusion," which preceded the introduction of this calendar, was prolonged to 445 days. The arrangement was somewhat upset by Augustus Caesar, who insisted that his month of August have as many days in it as that of Julius. Pope Gregory XIII finally corrected the Julian calendar by what is known as the Gregorian rule of intercalation, which was adopted by all Christian countries, except Russia which did not adopt it until 1918. It is: every year divisible by 4 without a remainder is a leap year; excepting Centurial years, which are leap years only when divisible by 4 after the omission of the two ciphers. This still leaves a gain of a day in 3,323 years, which suggests this further addition to the rule: Excepting that a year that is divisible by four after the omission of three ciphers is not a leap year. More exact, and almost as simple would be the rule of a leap year every fourth year for 31 leap years – suppressing the 32nd, which means merely the addition of 31 days every 128 years. This approximates the system which Omar Khayyam, astronomer to Sultan Jelal lid-Din of Persia, devised about 1079 A.D.

See also:
♦ Year ♦ Calendar ♦ Gregorian Calendar ♦ Julian Calendar ♦ Hebrew Calendar


Astro*Index Copyright © 1997 Michael Erlewine


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