The net effect was to add 22 or 23 days to the year, forming an intercalary year of 377 or 378 days.
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However, our sources very rarely tell us which years were regular, which were intercalary, and how long an intercalary year was.
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The intercalary day in a leap year is known as a leap day.
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The year consists of 19 months, each having 19 days, with four or five intercalary days, to make a full solar year.
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To keep a 12-month lunar year in pace with the solar year, an intercalary 13th month would have to be added on seven occasions during the nineteen-year period.
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The provision of adding an intercalary month to the year when needed had not been applied consistently, because it affected the length of terms of office.
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This has led to a superstition that intercalary months in certain times of the year bring bad luck.
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The reason for this is that a year is not evenly divisible by an exact number of lunations, so without the addition of intercalary months the seasons would drift each year.
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The ancient Egyptian civil year was 365 days long, and apparently did not have any intercalary days added to keep it in alignment with the Sothic year, a kind of sidereal year.