Calendars are something we all use in our daily lives, and are an essential part of
a functioning society. While modern calendars on your smartphone are a fairly recent innovation,
calendars themselves have been around since ancient times, first used more than 3000 years ago!
There have been hundreds of calendars throughout history, with many of these in use even to
this day. However, the calendar that is by far the most widely used, and probably the
one most of us know, is the Gregorian calendar.
Developed in 1582, named after Pope Gregory the 13th, the Gregorian calendar is actually
almost identical to the previously used Julian calendar, in use since Roman times. The only
difference is the way in which the calendars deal with leap years.
The Julian calendar had a leap year every 4 years because the time it takes the Earth
to revolve around the Sun is 365 and a quarter days. So with 3 years of 365 days and 1 with
366, this averages out to 365.25 days over a 4-year cycle. Problem solved.
Unfortunately, a solar year is actually 365.24217 days. This minor difference may seem insignificant,
but over the course of hundreds of years, it becomes significant. The Julian calendar
had slowly fallen out of sync with the Earth’s movement around the sun.
The problem here is that in the Christian year, Easter falls on the first Sunday after
the first full moon after the March equinox. However, by 1582, the calendar had diverged
from when this rule was established. To ensure that Easter would always be celebrated at
the same time of year as it historically had, Pope Gregory adjusted the rule for which years
are leap years.
As with the Julian calendar, a leap year would happen every 4 years... except for years that
are divisible by 100… except except years that are also divisible by 400. So for example,
the years 1800 and 1900 were NOT leap years, but 2000 was. The Julian calendar drifted
by 11 minutes per year, or 1 day every 128 years. The Gregorian calendar drifts just
27 seconds per year, accurate to 1 day in 3200 years.
Of course, to account for the difference in time that had already accumulated, the Gregorian
calendar was established already offset by 10 days from the Julian calendar. To get back
into sync, countries that have adopted the new calendar have had to skip forward for
the difference in days.
Not all countries did this initially. It was actually another 170 years before the British
Empire and their colonies adopted the new calendar, by this time 11 days out of sync.
Even later, it was the 20th century before Russia and Turkey switched, both having to
move forward 13 days.
Now, there was one country, Sweden, that didn’t want the major inconvenience of jumping forward,
disrupting monthly salaries, rent, and so on, so instead, decided to skip ahead gradually.
This would be achieved by omitting the 11 leap days from 1700 to 1740, bringing them
in-line with the Gregorian calendar and the other countries using it.
It was a good plan, and it would have worked… but things didn’t turn out that way. After
dropping the first leap day in February 1700, distractions of war caused the plan to be
abandoned and the years 1704 and 1708 were leap years. This caused Sweden to be out of
sync with both calendars… 1 day ahead of the Julian, but still 10 days behind the Gregorian.
To fix this, in 1712, Sweden had a double leap year - adding not only February 29th,
but also February 30th. Sweden eventually switched to the Gregorian calendar the normal
way, by skipping ahead 11 days in 1753.
Now, these calendars are examples of solar calendars—they’re based on the Sun. However,
some calendars also take the Moon’s movement around the Earth into account. These are known
as “lunisolar” calendars. Probably the best known example of this is the Chinese
calendar.
While the Gregorian calendar is used in China for civil purposes, the traditional calendar
is still used for determining Chinese festivals and celebrations. For example, the Chinese
New Year takes place on the 2nd (or 3rd) new moon after the winter solstice. Therefore
both the Sun and Moon must be used to figure out the date.
The calendar has 12 months of 29 or 30 days, alternating month-to-month. This is because
a lunar month is approximately 29½ days long. Months begin with the new moon, when the moon
is at its darkest, beginning its lunar phases over again.
Of course, this only adds up to 354 days, much too short for a solar year. To also stay
in sync with the Sun, the Chinese calendar also has leap years… but instead of having
a leap day, it has a leap month, in which one of the months of the year will be repeated
(and this can be any month). There’s a complex method of determining when a leap month should
be added, which I won’t go into, but the next leap month will begin on the 23rd of
May, 2020, in which the 4th month of the calendar will be repeated.
Now, what the Chinese calendar is probably most famous for, is the 12 animals of the
zodiac. Every year is assigned one of these animals, and follows this list, in order,
from year-to-year. For example, at the time of uploading this video, we’re coming to
the end of the Year of the Pig. January 25th, 2020 will mark the beginning of the Year of
the Rat, as the 12-year cycle starts over again.
A person born in a given year becomes associated with the animal of that year. For example,
if you were born in 1992 (after February 3rd), then you would be a monkey. If you were born
the following year, you’d be a rooster.
These animals are not thought of as arbitrary in Chinese culture, far from it. In fact,
millions of people place great importance on the animals of the zodiac. Often major
life decisions, such as getting married, having children, starting a business etc. can be
influenced by the animal of a particular year. Some animals are viewed as better than others.
Unsurprisingly given Chinese art and culture, the dragon is considered the best. If you
were born between any of the following dates, then congratulations, you’re a dragon. Noticeable
population spikes happen every 12 years in China as parents want their kids to be born
dragons.
Conversely, the worst animal is considered to be the goat. So much so that there were
actually reports in January 2015 of a surge in C-sections, as pregnant Chinese woman raced
to have their baby before the Year of the Goat began in February... If you were born
between any of these dates, you’re a goat. I wouldn’t worry too much, though, Bill
Gates is a goat, and he seems to be doing alright for himself…
Now, these zodiac animals are known as the “12 Earthly Branches”. These run concurrently
with what are known as the “10 Heavenly Stems”, comprised of two parts: 5 elements
(wood, fire, earth, metal, water) and either yin or yang. So as well as an animal, years
are also assigned one of the heavenly stems. These 12- and 10-year cycles are used in combination
to form a “sexagonary cycle” - a cycle of 60 years, ie - how long it takes before
the years repeat.
The current year, 2019, is jǐ-hài – yin earth, year of the pig. This is year 36 in
the current cycle, which began way back in 1984, and will finish in 2044.
Another lunisolar calendar is the Hebrew calendar. We’re currently in the year 5780, effectively
dating from what was established to be the creation of the world. Like the Chinese calendar,
this one also has 12 lunar months, with a 13th leap month to keep up with the Sun.
The calendar actually has two different New Years. The New Year for the civil, agricultural
year, occurs on the 1st of Tishrei, which is actually one of the most important Jewish
holidays, Rosh Hashanah. Biblically though, the 1st of Nisan is described as the New Year,
but this is only observed by a handful of Jewish communities. These usually occur on
September and March, respectively.
What’s peculiar about this calendar is that days don’t start at the same fixed time
every day, The beginning of a day is actually at sunset. This is based on interpretations
from the Book of Genesis – “there was evening and there was morning, one day”.
These last two calendars incorporated a lunar element, but they were tied to the sun overall.
However, the Islamic calendar, aka, the Hijri calendar is based purely on the Moon – a
lunar calendar. It has 12 lunar months of 29 or 30 days, but with no leap month since
it doesn’t stay in-line with the Sun. As with the lunisolar calendars, months begin
at the new moon, which is based on actual observation of the so-called “waxing crescent”,
as it’s known in astronomy.
One of these months has particular significance in Islam, and that is the 9th month – Ramadan,
which you’ve probably heard of. This is when Muslims around the world fast from sunrise
to sunset, abstaining from eating and drinking during daylight hours. This is one of the
the five pillars of Islam.
What’s interesting is that because the calendar is entirely lunar based, and only has 354
days, the date at which Ramadan starts changes from one year to the next, moving backwards
every year in relation to the Gregorian calendar.
So this means that fasting will have varying degrees of difficulty depending on the season
in which Ramadan happens to fall on a given year. While the difference is somewhat negligible
in Mecca, Muslims living further from the equator will see a much more pronounced difference,
with days being shorter in winter, but longer in summer. For example, just a few years ago,
Ramadam took place in June, and for those living in, say, Northern Europe, the sun can
be out for more than 16 hours per day, even up to 18 in some places. This would make fasting
incredibly challenging. On the flip side, of course, fasting is much easier in the winter
when the days are at their shortest, when the sun sets in the mid-afternoon.
Now, the Mayan calendar, is an interesting one. The Maya were a pre-Columbian civilisation
from Mesoamerica, and their calendar is among the oldest in existence. The calendar is quite
complex, it’s actually more of a calendar system comprised of two separate parts: the
Tzolk’in, and the Haab’.
The Tzolk’in is for keeping track of days. Each day is assigned a name and a number.
There are 20 day names, and they’re numbered from 1 to 13. This creates a cycle of 260
days, until all combinations of names and numbers have been made, and the cycle starts
over again.
The other part, called the Haab’, is made up of 18 months of 20 days… plus a random
5 extra days at the year which are supposedly unlucky. Although oddly, dates in a month
are given from 0 to 19. This totals 365 days, but with no leap years, it does not stay in
sync with the sun... if that was the intention.
If we combine the Tzolk’in and the Haab’ together we get to the day and the date. For
example, the 1st of January, 2020 would be: 10 Manik, 15th of K'ank'in, and the days following
would therefore be as such.
These day/date combinations are unique in the short-term, taking another 52 years before
being repeated. This is the length of the entire cycle of both the Tzolk’in and the
Haab’. One completion of this whole cycle is called a “Calendar Round”.
But how did the the Maya keep track of years over very long periods of time, like centuries
and millennia? This is where we use the Mesoamerican “Long Count” calendar. This numerical
calendar keeps track of years, months, and days passed since the supposed creation of
the world – roughly 4,000 years ago.
The Mayan word for a day was “kʼin”. Twenty of these kʼin are known as a winal.
Eighteen winal make a tun… twenty of these a k’atun, and 20 of these, a b’ak’tun…
and so on...
That last one, though, is important. As this is what led some people to believe the world
was going to end in 2012. December 21st, to be exact, as this was the day in which the
13th b’ak’tun came to an end. Given the superstition around the number 13, which also
had significance in Mayan culture, too… some had interpreted this to mean the Maya
had predicted the end of time. In reality, of course, it was just the beginning of the
14th b’ak’tun, and the Long Count calendar continued as normal. Given that a b’ak’tun
is a near 400-year cycle, the date certainly had significance, but was likely a cause for
celebration, rather than any kind of doomsday panic. It could perhaps be thought of as somewhat
comparable to the whole Y2K fiasco. Some hysteria and confusion, but ultimately it was just
an arbitrary date invented by humans with no real meaning to the universe itself.
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