CALENDARS, JUST IN THE NICK OF TIME

 I’ve been on a calendar, but I’ve never been on time. ~ Marilyn Monroe

Today’s date is November 13, 2021, as well as Alban 22, 1400, October 31, 2021 and 2459532.18830. I’ll explain each of these “today’s” dates shortly. There’s a long, fascinating history behind this date, and for that matter, any calendar date.

Several noteworthy events have occurred on November 13, including:

1775 - During the American Revolution, US forces captured Montreal.

1956 - The US Supreme Court struck down laws calling for racial segregation on public buses.

1971 - The US spacecraft Mariner 9 became the first spacecraft to orbit another planet, Mars.

1995 - Greg Maddox of the Atlanta Braves became the first major league pitcher to win four consecutive Cy Young Awards.

Why do we know when these events happened? Because of calendars. A calendar is a methodical ordering of days, months and years. Many diverse calendars, using different day-ordering systems, have been and are still being used. Calendar cognoscenti say there are about 40 different calendars now being utilized around the globe. Wikipedia displays an impressive 86 calendars in its list.

The word “calendar” is derived from calendae, the Roman designation for the first day of the month, when debts were due to be paid. I was told the “…ar” ending in the word calendar, which is much rarer than the usual “…er” ending syllable, notes a Sumerian dialect as its prime source.

For the past 439 years, virtually all of us have been using the Gregorian calendar as a basis for defining our day-to-day lives through the years. Ever since homo sapiens gained some sense of awareness of their larger surroundings – at least one hundred thousand years ago, perhaps much longer ago – they noted the daily cycle of each day, the roughly monthly cycle of the moon (29.53 days) and earth’s yearly cycle around the sun (365.242190 days in 2021).

The passage of the moon and the sun have always been the most prominent, regular, repeated events useful for keeping track of time. Virtually every human calendar uses some combination of lunar or solar periodicity, which is why many calendars are called lunisolar, whose date indicates both the moon phase and the time of the solar year.

Subsequent to the initial development of written records in the Near East, the first documented calendars are Bronze Age Sumerian/Babylonian calendars from 12,000 years ago. These calendars’ years began during the spring season with each of their lunar months (starting with a setting, new crescent moon), plus an intercalary “leap month” that could be inserted by decree. The intercalary period served to inflate the year’s number of days, allowing the annual calendar to follow the seasons. Such adjustments were important because the shorter 12 lunar months add up to almost 11 fewer annual sidereal days.

The Babylonian calendar was followed by Zoroastrian and Persian ones. Evidence of Persian calendars has been found from the second millennium BCE. Persian calendars have been altered many times for a variety of religious and administrative motivations. The calendars’ twelve 30-day months were each named for festivals or activities during the year. An intercalary phase was added periodically to harmonize the calendar with the seasons.

The 11th-century Persian intellect Omar Khayyam – a true Renaissance man, several centuries or so before its time in Italy – lay the formulation and structure for one of the most accurate, ancient calendars. In 1079, Khayyam made astronomical observations and announced a new calendar whose year-length was measured as 365.242198 days. This 942-year-old estimate represents astounding accuracy, fully comparable to modern calculations. Today’s date is Alban 22, 1400 in the Persian calendar.

The Persian year usually begins within a day of the northern vernal equinox, March 20-21 in the Gregorian calendar. The Persian calendar was one of the first to be based on the solar year, rather than a lunar or lunisolar approach. That’s consistent with the sun’s being a divine and religious symbol in Persian culture.

The Hindu calendar has been guiding people on the Indian continent probably since 1700 BCE and continues to be used by Hindus around the world to determine festival dates. The ancient Hindu calendar ordering system is also seen the Babylonian calendar, as well as the Hebrew and Chinese calendars.

The Hindu system differs from the Gregorian calendar. Unlike the initial Gregorian calendar, which added days to several lunar months to synchronize lunar cycles and the sidereal year, the Hindu calendar maintains every lunar month, and inserts a full-month intercalary period every 32–33 months. This ensures that festivals and agriculture-related rituals that are spread throughout the year occur during the appropriate season. An elegant Hindu calendar from 1871 is shown below.

 

Hindu calendar

The first Roman calendars also followed lunar month cycles. Each month had several principal days, including the first day (the kalends) and a day a bit before the middle of the month (the ides). Thus, these calendars had more ides beyond just March. For centuries, the Romans had eight-day weeks, two millennia before the Beatles’ song.^[1] It wasn’t until 321 CE that Emperor Constantine eventually established a seven-day week in the Roman calendar.

Interestingly, the Babylonians were astute observers of the skies, and it is largely thanks to them that Constantine changed the week’s length. The reason the Babylonians first adopted seven days was they saw seven celestial bodies that were deemed preeminent — the sun, the moon, Mercury, Venus, Mars, Jupiter and Saturn. The chart below shows how each of the seven weekdays were named.

Weekday	Named after
Sunday	the celestial body, Sun.
Monday	the celestial body, Moon.
Tuesday	Tiu, the Anglo-Saxon god of war. The Romans named their third day of the week after Mars, their god of war. That is why romantic languages like Spanish, French and Italian all have similar names for Tuesday: martes, mardi, and martedi.
Wednesday	Woden, the Norse god of war.
Thursday	Thor, the Norse god of thunder and lightning.
Friday	Frigg, the wife of Woden, representing love and beauty.
Saturday	Saturn, the Roman god of agriculture.

 Way before Constantine, Julius Caesar reformed the Empire’s existing calendar in 45 BCE with help from Greek mathematicians. This new calendar, the Julian calendar, became a solar calendar. Today’s Julian calendar date is Oct. 31, 2021, Halloween (again)!

Two changes were made. Simply put, the first modification realigned the Julian calendar year to be consistent with a solar year and became 365 days long. This was done by inflating the number of days in several old Roman months. Second, a leap day was added to February every four years, making average Julian year-length, 365.25 days. And eventually, the seventh month turned into July (after Julius Caesar) followed by August (after Caesar Augustus).

The Julian calendar became the principal calendar in the Roman Empire and subsequently in most of the Western world for more than 1,600 years.

However, the Roman Catholic Church noticed that the Julian system had caused the calendar to drift relative to the spring and fall equinoxes. This was important because the Julian calendar’s excess leap days caused the northern hemisphere’s spring equinox to happen considerably before March 20 or 21 and thus affected the church’s crucial spring celebration, the lunar-based Easter Sunday mass^[2].

With such motivation, Pope Gregory XIII proclaimed in 1582 a minor but crucial calendar modification which reduced the average length of the Julian year from 365.25 days to 365.2425 days. The Gregorian calendar thus more closely approximates the 365.242190-day solar year that it takes the Earth to make one revolution around the Sun.

The Gregorian calendar change does this by spacing leap years beyond the Julian method of simply saying a leap year is one that is exactly divisible by four. Gregorian leap years include the Julian method, but go beyond it. The further delineation for Gregorian leap-years is for years which are exactly divisible by 100, like 2000 was. These years are only a leap year if they are exactly divisible by 400. Thus, the century year that will begin on Friday, Jan. 1, 2100 is not a Gregorian leap year nor was 1900. But 2000 was and 2400 will be. Consequently, the Gregorian calendar corrected the Julian calendar's wandering away from the solar year and has been with us on our spinning globe ever since 1582.

Another calendar mechanism is the Julian day. No, it’s not an update of the ancient Julian calendar. The Julian day format, also called the ordinal format, is yyyyddd (first four digits signify the year, the next three refer to the numeric day of the year). Today’s Julian day date is thus 2021313. The format is used in computer programming and by the military.

Confusingly, there is also a Julian Date Number (JDN) used by astronomers, other skyward-looking scientists and in software. It is the strangest calendar mechanism I found. This date is today’s contiguous number of days, and fractions of days, since the beginning of the Julian Period, which is defined at noon Universal Time on Jan. 1, 4713 BCE. Really? Today’s JDN, at 08:30 PST (drum-roll please) is 2459532.18830, which is a whole lot of days and digits.

Why Jan. 1, 4713 BCE? Because Joseph Scaliger devised this calendar mechanism in 1583, one year after the Gregorian calendar began. And he chose the Julian Period to begin on the date when the Julian calendar, the Lunar calendar and the Roman Tax calendar all coincided – Jan. 1, 4713 BCE. Also, this date apparently is the most recent day in which the year began on a Sunday with a full moon.

No matter how you choose to label today, I hope it’s a good date for you.

 

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[1] The Beatles’ Eight Days a Week was recorded in 1964: “Hold me, love me, hold me, love me, I ain't got nothing but love, babe, eight days a week.”

[2] The date of Roman Catholic Easter is the Sunday on or after the first full moon following the spring equinox.