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Every Monday morning at 6:49 and 8:49, IPR News Radio looks into the night sky with Mary Stewart Adams, former Program Director and founder of the International Dark Sky Park at the Headlands, who has been telling stories of the night sky on IPR since 2013.

On 'Sextilis Kalends Martias' Leap Day was Instated: this week on the Storyteller's Night Sky


Were it not for the significant 16th century event that took place on Monday of this week, then we’d be reckoning time according to a different date come Saturday, which is Leap Day, February 29th, a date that only rolls around once every four years, providing the year is divisible by 400.

In 1582, after centuries of trying to account for the discrepancy between the solar and lunar rhythm so as to create a calendar in which the sacred festivals could be placed in the right season in the right month and on the right day, the Catholic Church issued the Gregorian Calendar Reform.

To the Babylonians was owed the division of the year into 12 months. To the Jewish tradition was owed the practice of measuring the month from the first visibility of the New Moon, and to both the Jewish and Egyptian traditions was owed the practice of introducing an extra month in order to keep the festivals aligned to the seasons.

One of the first big calendar reforms was done by Julius Caesar in the 1st century BC, and even though he included leap days in his system, there were still errors, and so the Gregorian Reform, issued on February 24, 1582. The date of issue in the old form was “sextilis kalends Martias”, or six days before the beginning of March, which is February 24th.

It took nearly 400 years for the Gregorian calendar to become the global civic calendar, which ultimately allows for the global economy in which we find ourselves. In fact the word calendar derives from “kalendaria” which was essentially an accounting book used in ancient Rome and into which were inscribed the debts that had to be paid at the first of every month, which was known as the kalends.