February 29 takes approximately 6 hours longer than 365 whole days. A leap day compensates for this lag, realigning the calendar with the Earth's position in the Solar System; otherwise, seasons would occur later than intended in the calendar year. The Julian calendar used in Christendom until the 16th century added a leap day every four years; but this rule adds too many days (roughly 3 every 400 years), making the equinoxes and solstices shift gradually to earlier dates. By the 16th century the vernal equinox had drifted to March 11, and the Gregorian calendar was introduced both to shift it back
Middle-earth calendar is year 1421 on the Shire calendar. A year in the Shire is the same length as our year – 365 days, 5 hours, 48 minutes, 46 seconds. The Shire's calendar year is also divided into 12 months but all of 30 days. Five additional days are added to create a 365-day year. For the names of the months, Tolkien used reconstructed names derived from the Anglo-Saxons; in other words, they are Tolkien's take on what English would be actually using now if it had not adopted Latin names for the months (January, February, March, etc.). The "Yuledays" are the