Historia, filosofía-biografia-pensamiento

The Julian calendar, also called the Old Style calendar, is a dating system established by Julius Caesar as a reform of the Roman republican calendar. Caesar, advised by the Alexandrian astronomer Sosigenes, made the new calendar solar, not lunar, and he took the length of the solar year as 365¼ days. The year was divided into 12 months, all of which had either 30 or 31 days except February, which contained 28 days in common (365-day) years and 29 in every fourth year (a leap year, of 366 days). Because of misunderstandings, the calendar was not established in smooth operation until AD 8. Further, Sosigenes had overestimated the length of the year by 11 minutes 14 seconds, and by the mid-1500s, the cumulative effect of this error had shifted the dates of the seasons by about 10 days from Caesar’s time. This inaccuracy led Pope Gregory XIII to reform the Julian calendar. His Gregorian calendar, also called the New Style calendar, is still in general use. Gregory’s proclamation in 1582 r...

The measure of time on which the calendar is based. It is the time taken for the earth to complete one orbit of the sun. The calendar year consists of an average of 365.25 mean solar days – three successive years of 365 days followed by one (leap) year of 366 days. The solar year (or astronomical year) is the average interval between two successive returns of the sun to the first point of Aries; it is 365.242 mean solar days. The sidereal year is the average period of revolution of the earth with respect to the fixed stars; it is 365.256 mean solar days. The anomalistic year is the average interval between successive perihelions; it is 365.259 mean solar days. [1] See also in Spanish, Año . [1] Year. In a Dictionary of Science, FIFTH EDITION. Oxford University Press Inc., New York, 2005.