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Credit & Copyright: Rune Rysstad
Explanation:
Even as leap days go, today is a remarkable one.
In 46 BC,
Julius Caesar, pictured above in a self-decreed minted coin,
created a calendar system that added one
leap day every four years.
Acting on advice by Alexandrian astronomer
Sosigenes, Caesar did this to make up for the fact that the
Earth's year is slightly more than 365 days.
In modern terms, the time it takes for the Earth to circle
the Sun is slightly more than the time it takes for the
Earth to rotate 365 times (with respect to the Sun -- actually
we now know this takes about 365.24219 rotations).
So, if calendar years contained 365 days they would drift
from the actual year by about 1 day every 4 years.
Eventually July (named posthumously for
Julius Caesar himself)
would occur during the northern hemisphere winter!
By adopting a leap year with an extra day every four years, the
calendar year would drift much less.
This Julian Calendar system was used until the year 1582 when
Pope Gregory XIII added that leap days
should not occur in years ending in "00" except
if divisible by 400, providing further fine-tuning.
This Gregorian Calendar system is the one in common use today.
Therefore, even though this year 2000 ends in "00", it remains a
leap year, and today is the added leap day.
That makes today the first leap day
for a centurial year since year 1600 and the second
such leap day of the Gregorian Calendar.
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Based on Astronomy Picture
Of the Day
Publications with keywords: Julius Caesar - Leap Days
Publications with words: Julius Caesar - Leap Days
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