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Leap years add an extra day to keep calendars in sync with seasons and astronomical events. The Gregorian calendar adds a day every four years except for years ending in -00, unless they are divisible by 400. Other calendars have different methods for adding leap years, with varying degrees of accuracy. Leap years have traditions and superstitions, such as women proposing marriage and February 19 being an unlucky day. People born in leap years usually celebrate their birthdays on February 28.
A leap year, also known as a leap year, is one that contains an extra day, usually February 29, although this varies in some calendars. In the Gregorian calendar, which is used by most of the world, a leap year occurs every four years, or 97 years out of every 400. This is one way to keep the seasons, astronomical events, and time differences in sync. Without leap years, the Gregorian calendar would lose its validity in just over a hundred years, leading to time differences between day and night, and bringing forward the equinox.
The Gregorian method adds a 29th day in all years divisible by 4 except for years ending in -00, such as 1900 or 2100, the extra day is not added. However, there is one more exception to the exception: for years ending in -00 that can be divided by 400, the extra day is added. The years 1600 and 2000, for example, were leap years, as will 2400. This approach makes the Gregorian method the most accurate way to create leap years, allowing it to fall behind only one day every 8,000 years.
Other calendars don’t do a very good job of creating leap years. Examples are the Julian and Coptic calendars, which create leap years by simply adding an extra day every four years, regardless of any other considerations. This method, in common use until a few centuries ago, advanced the calendar by one day every 130 years.
The Jewish calendar, which is lunisolar, adds an extra month rather than an extra day to form a leap year. This is done using a complicated rule, creating seven leap years every nineteen. Since the first day of the Jewish new year cannot fall on a Wednesday, Friday, or Sunday, the rules adjust according to the year, so it’s hard to estimate when a leap year will come. Other calendars that add leap days include the Indian National Calendar (one extra day in February/March), the Hindu calendar (one extra month, added when two dark moons occur), and the Chinese calendar (one extra month added using a complicated lunar system).
There are several traditions and superstitions based on leap years. An ancient Irish legend says that women are only allowed to propose marriage on leap years; men must take the lead at any other time. Other traditions considered February 19 as an unlucky day in which new businesses, travel and partnerships should not be started. People born in leap years usually celebrate their birthdays on February 28, which is usually considered their legal birthday.
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