- 4374 -
WHY A LEAP
YEAR - ?
February 29, 2024, why is this a leap year? Astrophysicists explain this
month's extra day? Many people will
know this means that February gets a total of 29, as opposed to 28, but, they
often do not know why.
-
-------------------
4374 - WHY
A LEAP YEAR - ?
-
- Leap years play a
crucial role in aligning our calendar with the Earth's orbit around the sun.
The orbit, otherwise known as a “tropical year”, takes about 365.24 days to
complete. This is slightly longer than our standard calendar year of 365 days.
-
- This extra quarter
of a day each year may seem insignificant, but over time, it adds up, leading
to a noticeable shift in our calendar.
Without adjusting for this extra time, our calendar would gradually fall
out of sync with the astronomical seasons, causing a significant drift over the
years. Leap years are essential to prevent this drift and maintain the
alignment of our calendar with the Earth's journey around the sun.
-
- To counter this
misalignment, the leap year system adds an extra day to the calendar every four
years. This adjustment is made by extending February to 29 days. This seemingly
simple solution of adding a day every four years is refined further in the
Gregorian calendar, the most widely used calendar system today.
-
- Leap years were
incorporated as far back as the Roman times when a year was separated into 12
months (365 days). In the year 46 BC,
Julius Cesar proposed the new Julian Calendar, which would add an additional
day to the shortest month of the year (February) every four years in an attempt
to allow for a predictable correction to the issue of the quarter day drift.
-
- However, this was
actually a slight overcorrection to the problem. As the solar year was not
exactly 365.25 days but was, in fact, slightly less at 365.2422 solar days, the
Julian Calendar and the solar year were now drifting apart again, albeit much
more slowly, at a rate of 11.2 minutes per year.
-
- By the late 1500s,
this small over correction in the Julian calendar had accumulated to a drift of
13 days with respect to the solar year. Cue Pope Gregory XIII, the Pontifex
Maximus of the Catholic church at the time. In 1582 he gave us the Gregorian
calendar, which modified the Julian Calendar to account for the 11.2-minute
drift. Many countries, including the UK, still use the Gregorian calendar
today.
-
- To improve upon the
over-correction made by the Julian calendar, the Gregorian calendar skips three
leap days every 400 years. This gives an average year of 365.2425 solar days
which is much closer to the solar year of 365.2422 solar days.
-
- Leap years
beautifully illustrate how we have harmonized our constructed concept of time
with the natural rhythm of the universe, maintaining a critical balance between
human activities and the Earth's natural cycles.
-
- The math is
mind-boggling in a layperson sort of way and down to fractions of days and
minutes. There's even a leap second occasionally, but there's no hullabaloo
when that happens.
-
- The thing to know
is that leap year exists, in large part, to keep the months in sync with annual
events, including equinoxes and solstices.
It's a correction to counter the fact that Earth's orbit isn't precisely
365 days a year. The trip takes about six hours longer than that.
-
- Contrary to what
some might believe not every four years is a leaper. Adding a leap day every
four years would make the calendar longer by more than 44 minutes. Later, on a calendar yet to come (we'll get
to it), it was decreed that years divisible by 100 not follow the four-year
leap day rule unless they are also divisible by 400, the JPL notes. In the past
500 years, there was no leap day in 1700, 1800 and 1900, but 2000 had one. In
the next 500 years, if the practice is followed, there will be no leap day in
2100, 2200, 2300 and 2500.
-
- The next leap years
are 2028, 2032 and 2036. Ancient
civilizations used the cosmos to plan their lives, and there are calendars
dating back to the Bronze Age. They were based on either the phases of the moon
or the sun, as various calendars are today. Usually they were
"lunisolar," using both.
-
- The Roman Empire
and Julius Caesar was dealing with major seasonal drift on calendars used at
the time. They dealt badly with drift by adding months. He was also navigating
a vast array of calendars starting in a vast array of ways in the vast Roman
Empire.
-
- Caesar introduced
his Julian calendar in 46 BCE. It was purely solar and counted a year at 365.25
days, so once every four years an extra day was added. Before that, the Romans
counted a year at 355 days, at least for a time.
-
- But still, under
Julius, there was drift. There were too many leap years! The solar year isn't
precisely 365.25 days! It's 365.242 days.
-
- Adding periods of
time to a year to reflect variations in the lunar and solar cycles was done by
the ancients. The Athenian calendar was used in the fourth, fifth and sixth
centuries with 12 lunar months. That
didn't work for seasonal religious rites. The drift problem led to
"intercalating" an extra month periodically to realign with lunar and
solar cycles.
-
- The Julian
calendar was 0.0078 days (11 minutes and 14 seconds) longer than the tropical
year, so errors in timekeeping still gradually accumulated. The Julian calendar was the model used by
the Western world for hundreds of years.
-
- Enter Pope Gregory
XIII, who calibrated further. His Gregorian calendar took effect in the late
16th century. It remains in use today and, clearly, isn't perfect or there
would be no need for leap year. But it was a big improvement, reducing drift to
mere seconds.
-
- Easter was coming
later in the year over time, and the Pope fretted that events related to Easter
like the Pentecost might bump up against pagan festivals. The pope wanted
Easter to remain in the spring.
-
- He eliminated some
extra days accumulated on the Julian calendar and tweaked the rules on leap
day. It's Pope Gregory and his advisers who came up with the really gnarly math
on when there should or shouldn't be a leap year.
-
- If the solar year
was a perfect 365.25 then we wouldn't have to worry about the tricky math
involved.
-
- The leap day comes
with lore about women popping the marriage question to men. It was mostly
benign fun, but it came with a bite that reinforced gender roles. One story places the idea of women proposing
in fifth century Ireland, with St. Bridget appealing to St. Patrick to offer
women the chance to ask men to marry them.
-
- Being born in a
leap year on a leap day certainly is a talking point. But it can be kind of a
pain from a paperwork perspective.m There are about 5 million people worldwide
who share the leap birthday out of about 8 billion people on the planet.
-
- This year is
different. Without the leap years, after
a few hundred years we will have summer in November. Christmas will be in summer. There will be
no snow. There will be no feeling of Christmas.
Leap years are necessary, get over it!
February 29, 2024
WHY A
LEAP YEAR -
? 4374
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Saturday, March 2, 2024 ---------------------------------
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