Leap Day: The Extra Day That Keeps the Calendar in Sync

Every four years, we add an extra day to the calendar in the form of February 29, also known as Leap Day. But why do we need this extra day, and what does it have to do with the Earth's movement around the sun? In this feature story, we will explore the history, purpose, and traditions of Leap Day, and how it helps us keep track of time and seasons.

What is Leap Day and why do we need it?

Leap Day is a day inserted into the calendar to make it more accurate.

The calendar we use today is based on the Gregorian calendar, which was introduced by Pope Gregory XIII in 1582 to replace the Julian calendar, which had been in use since 46 BC. The Julian calendar was based on the assumption that the Earth takes 365.25 days to orbit the sun, so it added a leap day every four years.

However, this was slightly too long, and over centuries, the calendar drifted away from the solar year, the time it takes for the Earth to complete one orbit around the sun.

The Gregorian calendar fixed this problem by introducing a more precise rule for leap years: a year is a leap year if it is divisible by four, except if it is divisible by 100 unless it is also divisible by 400.

For example, 2000 was a leap year, but 1900 was not. This rule makes the average length of a year 365.2425 days, which is very close to the actual solar year of about 365.2422 days.

By adding a leap day every four years, the Gregorian calendar keeps the calendar year aligned with the seasons, which are determined by the Earth's position relative to the sun.

How did Leap Day originate?

The idea of adding an extra day to the calendar to keep it in sync with the solar year is not new.

Many ancient calendars, such as the Hebrew, Chinese, and Buddhist calendars, used intercalary months instead of days, to account for the difference between the lunar cycles and the solar year.

The early Roman calendar, which consisted of 10 months plus a vague winter period, also used an intercalary month of 23 days, called Mercedonius, to adjust the calendar.

However, this system was not very regular, and the decision of when to insert the intercalary month was often influenced by political and religious factors.

The first leap day in the modern sense was introduced by Julius Caesar in 46 BC when he reformed the Roman calendar and created the Julian calendar. He replaced the intercalary month with a single intercalary day, which he placed after February 23, the sixth day before the calends of March.

This day was known as "bis sextum", meaning "twice sixth", and gave rise to the term "bissextile year" for leap years. Caesar also made the length of all months fixed, except for February, which had 28 days in regular years and 29 days in leap years.

The Julian calendar was widely used in Europe and other parts of the world for more than 1,500 years until it was replaced by the Gregorian calendar in the late 16th century.

The Gregorian calendar retained the concept of leap day but modified the rule for leap years to make the calendar more accurate and stable.

What are some traditions and superstitions associated with Leap Day?

Leap Day has inspired many customs and beliefs around the world, some of which are still practiced today. 

- In Ireland, Leap Day is known as Bachelor's Day, a tradition that dates back to the 5th century, when St. Brigid of Kildare asked St. Patrick to grant women the right to propose to men on Leap Day. According to legend, St. Patrick agreed, but only on the condition that the women had to wear either a red petticoat or a red skirt to signal their intention. The tradition was later brought to Scotland by Irish monks, where the parliament passed a law in 1288 that allowed women to propose to men on Leap Day. If the man refused, he had to pay a fine, which could range from a kiss to a silk gown. In some places, Leap Day is also called Sadie Hawkins Day, after a fictional character from a comic strip who chased after eligible bachelors.

- In Greece, Leap Day is considered an unlucky day to get married, as it is believed that such marriages are doomed to end in divorce. A similar belief exists in Italy, where the proverb "anno bisesto, anno funesto" means "leap year, doom year". Some people also avoid starting a new job or moving to a new house on Leap Day, as they fear it will bring bad luck.

- In France, Leap Day is associated with a humorous newspaper called La Bougie du Sapeur, which is published only once every four years, on February 29. The newspaper was created in 1980 by a comic book writer named Jacques Debuisson, who was inspired by the story of a fictional character named Sapeur Camember, a soldier who was born on February 29, 1844, and who joined the army on February 29, 1864. The newspaper features satirical articles, cartoons, and puzzles, and has a loyal following of readers who eagerly await its rare appearance.