What is the Leap Year Pattern?


Specific Question:







Fri, 24 Feb 2006 09:40:59 -0600

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My question is in regard to the actual number of solar days in a solar year,


I am only addressing the natural relationship between the Sun and the Earth from a fixed and anchored point,


This would be sunrise on the day of the spring equinox and from sunrise to sunrise for each day,


Therefore the actual number of solar days in a solar year will be a whole number, and have nothing to do with the many confusing calendars and man made divisions,


I find a repeating four (4) year pattern where every fourth year is made up of 366 solar days and the three years in between are made up of 365 solar days,


Am I correct in regard to this four year pattern ?




Defining the year, for Planet Earth is not easy. The average Gregorian Year is 365.2425 days, while the average Julian year is simply 365.25 days. When the Julian year was in use, most years had 365 days while every fourth year had 366 days.


However, by the time of Pope Gregory XIII in 1582, Easter was becoming very difficult to calculate as the Vernal Equinox had shifted from the traditional March 21, as the Julian year was not precise.  Hence with the Gregorian calendar reform, leap years were skipped in years ending in “00” except every fourth such year (i.e. years evenly divisible by 400). Hence, the years 1700, 1800, and 1900 were not leap years while the year 2000 was a leap year. All other years evenly divisible by four continue to be leap years.


Here is an Internet link, with an essay on the Gregorian Calendar Reform:


< http://www.polysyllabic.com/GregConv.html >


For more information, or a clarification, send your request to the following electronic mail address:
                                      < FAQ@planetarium.cc >.
Editor’s Note: This astronomically-related question was answered by Glenn A. Walsh, who served as
Astronomical Observatory Coordinator and a Planetarium Lecturer at Pittsburgh’s original
Buhl Planetarium and Institute of Popular Science in the late 1980s and early 1990s. Mr. Walsh also served as a Life 
Trustee, on the Board of Trustees, of the Andrew Carnegie Free Library and Music Hall in Carnegie, Pennsylvania in the 
late 1990s, including one year as the Library’s Treasurer.
Today, Mr. Walsh is Project Director of a not-for-profit organization, Friends of the Zeiss, which works for the
preservation and continued functionality of the historic equipment and artifacts of a
pioneer in the history of the development of planetaria and museums of the physical sciences, Pittsburgh's
Buhl Planetarium and Institute of Popular Science, including the Zeiss II Planetarium Projector,
now the oldest operable major planetarium projector in the world !
Glenn A. Walsh
Electronic Mail - < gawalsh@planetarium.cc > 
Author of History Web Sites on the Internet --
* Buhl Planetarium, Pittsburgh: 
  < http://www.planetarium.cc > 
* Adler Planetarium, Chicago: 
  < http://adlerplanetarium.tripod.com >
* Astronomer & Optician John A. Brashear: 
  < http://johnbrashear.tripod.com > 
* Andrew Carnegie & Carnegie Libraries: 
  < http://www.andrewcarnegie.cc > 
* Duquesne Incline cable-car railway, Pittsburgh: 
  < http://www.incline.cc >

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