Change year is the designation for a calendar year that deviates from the duration of the solar year and on this basis "wanders" through the seasons in the further course . The duration of the period after which the change year calendar again coincides with the actual seasons can be calculated through the respective temporal deviation of the change year from the solar year .
Ancient Egyptian calendar
The best-known example is the Egyptian calendar . In ancient Egypt , the difference between the 365-day administrative calendar and the solar year was a little less than a quarter day.
The Egyptian calendar knew, with the exception of four days under Ptolemy III. , no leap days. Due to the faster earth rotation , the value in 139 AD for the mean solar year was 365.2423 days.
Middle of the second millennium BC The duration of the mean solar year was 365.2424 days. With the calculation: 1 divided by (365.24235 days minus 365 days) you get 4.1263 years. In Egyptian practice, this meant that every 4.1263 years the climate (i.e. the concrete measurable inclination of the sun's orbit relative to the horizon) shifted back one calendar day in the Egyptian calendar. Multiplied by the Egyptian year length of 365 days, this results in a cycle of 1506 years. As a result, this means that after 1507 calendar years, which corresponded to 1506 tropical years , the ancient Egyptian calendar matched the actual seasons again .
- Thomas Vogtherr : Time calculation. From the Sumerians to the Swatch . Beck, Munich 2006, ISBN 3-406-44763-5 .
- ↑ Jean Meeus : More Mathematical Astronomy Morsels , Richmond 2002, equinoctial and Solstitialjahre: , ISBN 0-943396-74-3 , S. 362nd
- ^ Jean Meeus, D. Savoie: The History of the Tropical Year . In: The journal of the British Astronomical Association, Vol. 102, No. 1 . 1992 ( bibcode : 1992JBAA..102 ... 40M )