Which month gains an extra day during a leap year?

And the answer: February.  
Photo credit: public domain. 

The intercalary day, February 29, is added once every four years to keep our calendar year in pace with the solar year, which is nearly six hours longer than an exact 365 days. During "leap years," that extra time is made up by adding a day. Other planets also have leap years—in fact, Mars has more leap years than regular years to keep pace with the sun.

Every 365 days (and some change), our Earth completes a revolution around the sun. Yet, for around 1500 years, most of Europe adhered to Julius Caesar’s humbly named Julian calendar, which failed to correctly account for the extra time it takes for the Earth to complete its route around the sun. Turns out, a miscalculation of just 11 minutes meant that important holidays like Easter strayed farther and farther from the spring equinox.

When the Gregorian calendar was adopted in 1582, a number of important adjustments needed to be made. For one, those who used the Julian calendar (i.e. most of Europe) were about 10 days behind the actual solar calendar. This was fixed by simply skipping those dates. In North America, for example, the month of September in 1752 had only 19 days, as the day count went straight from September 2 to September 14. To make matters more complicated, only five countries adopted the new calendar system that year—namely Italy, Poland, Portugal, Spain, and most of France. Since the discrepancy between the Julian calendar year and the astronomical seasons kept growing over time in the centuries that followed, more days had to be skipped in countries that switched to the Gregorian calendar in later years. The US, Canada, and the UK dropped 11 days in 1752; Japan cut the year 1872 short by 12 days; and some countries, such as Russia, Greece, and Turkey, switched calendars as late as the early 20th century, so they had to omit 13 days.

Did you know?

Yesterday was New Year’s Eve! Civilizations around the world have been celebrating the start of each new year for at least four millennia. Today, most New Year’s festivities begin on December 31 (New Year’s Eve)—the last day of the Gregorian calendar—and continue into the early hours of January 1 (New Year’s Day). As we reflect on 2022 and look forward to the year ahead, we can at least be thankful that we finally have our calendars (more or less) figured out.
Learn more about the history of leap years and calendars here.

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