11-03-2014  (42036 lectures) Categoria: Articles

The Longest Night in History: The Transition from the Julian to the Gregorian Calendar

Title: The Longest Night in History: The Transition from the Julian to the Gregorian Calendar


The night from the 4th to the 15th of October 1582 is often referred to as "the longest night in history" due to the significant events that unfolded during this time. This period marked a pivotal moment in the history of calendars, as Pope Gregory XIII introduced the Gregorian calendar and brought about a reform that corrected inaccuracies in the Julian calendar. This transition not only impacted the way people measured time but also had profound religious and cultural implications. One of the notable figures who passed away during this transition was Saint Teresa of Ávila.

The Julian Calendar and Its Flaws:

The Julian calendar, established by Julius Caesar in 45 BCE, was used for centuries to measure the passage of time. However, it suffered from a significant flaw—a miscalculation in the length of a year. The Julian calendar consisted of 365.25 days, which was slightly longer than the solar year, causing a discrepancy of approximately 11 minutes and 14 seconds per year. Over time, these accumulated errors created a misalignment between the calendar year and the astronomical year, leading to the need for calendar reform.

Pope Gregory XIII's Reforms:

In an effort to rectify the inaccuracies of the Julian calendar, Pope Gregory XIII, with the help of astronomers and mathematicians, introduced the Gregorian calendar. The reform entailed several crucial changes:

  1. Dropping Days: The reform eliminated ten days from the calendar. To correct the accumulated errors, Thursday, October 4, 1582, was followed by Friday, October 15, 1582.

  2. Leap Year Adjustments: To maintain precision in tracking the solar year, the Gregorian calendar introduced a rule for leap years, stating that years divisible by 100 but not by 400 would no longer be leap years. This refined the Julian leap year system.

  3. Accuracy: The Gregorian calendar's average year length was 365.2425 days, which more closely approximated the actual length of the solar year.

Impact on Saint Teresa of Ávila's Death:

Saint Teresa of Ávila, a prominent Spanish mystic, and writer, died on the night of October 4, 1582, shortly before the transition to the Gregorian calendar. Her death, like many other historical events, was recorded according to the Julian calendar. Therefore, her death is often noted as occurring on October 4, 1582, though it would have been October 15, 1582, according to the Gregorian calendar. This discrepancy serves as a poignant example of the calendar reform's effects on historical records.


The night from October 4 to October 15, 1582, marked a turning point in the history of calendars. Pope Gregory XIII's introduction of the Gregorian calendar corrected the errors of the Julian calendar, aligning the calendar year more accurately with the solar year. The transition had far-reaching implications, affecting not only the measurement of time but also the recording of historical events, such as the death of Saint Teresa of Ávila. The "longest night in history" serves as a reminder of the evolving nature of our understanding of time and the importance of calendar accuracy in historical documentation.

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