Tag Archives: calendar

Bend me your years

Rome’s second king, Numa Pompilius, felt kind of bad about those unnamed extra winter days, so he came up with two new months: Januarius and Februarius. King Numa tacked his new months onto the beginning of the year, which bumped all the other months back. That wasn’t such a big deal for the first four months, which were named for gods (Mars, Aphrodite, Maia, Juno)—but it’s darned awkward for the other months, which were named for their numbered positions in the year. ‘September’ means ‘seventh month’ but now it’s the ninth. October means eighth, but it’s the tenth. November means ninth, but it’s the eleventh. December means tenth, but it’s the twelfth.

The calendar year still kept coming up 10 days too short, so every 2-3 years a leap month—Intercalaris—was added.

In 45 bc, Julius Caesar reformed the Roman calendar by uncoupling it from the Moon—no more figuring out lunar cycles. He must have decided that having a set number of days in a year—365—meant fewer headaches when running something as big as the Roman Empire. Julius ditched the leap month. But because a year is actually 365 days and 6 hours, he added an extra day (February 29) every fourth year—the Leap Year.

What about Quintilis and Sextilis? Quintilis (means ‘fifth month,’ now it’s the seventh) was renamed July for Julius Caesar and Sextilis (means ‘sixth month,’ now it’s the eighth) was renamed August for Caesar Augustus (Julius’ nephew and Rome’s first emperor).

This was the Julian Calendar. It’s more or less the same one we use today.

Julius Caesar reforming the calendar.

Romulus’ days were numbered

Romulus’ 10-month calendar featured adorable wolf puppies on every slab.

The original Roman calendar was invented by Romulus, the first king of Rome, around 753 bc. The calendar started the year in March (Martius) and consisted of 10 months, with 6 months of 30 days and 4 months of 31 days. The winter season didn’t get any months with names, so the calendar year only lasted 304 days with 61 extra days in the winter. Everybody stayed home during those 61 days and looked at seed catalogues.

Here are the months of Romulus’ calendar:

Martius – 31 Days
Aprilis – 30 Days
Maius – 31 Days
Junius – 30 Days
Quintilis – 31 Days
Sextilis – 30 Days
September – 30 Days
October – 31 Days
November – 30 Days
December – 30 Days

Back to the beginning of The Western Civ User’s Guide to Time & Space

We locked a bunch of astronomers in a room and you’ll never believe what happened next!

Roman astronomers trying to get the lunar and solar cycles to match up. I threw a couple of Sun-worshiping Druid priestesses in there, too.

A big headache with ancient calendars is that they had to be constantly updated to make them agree with the movements of both the Moon and the Sun. Months are based on the Moon’s cycles. Years are based on Earth’s orbit around the Sun. ‘Calendae’—we say ‘calends’—is a Latin word for ‘first day of the month.’ ‘Ides’ is the day in the middle of each month. Astronomers (scientists who study the stars and planets) would first determine the ides (when the moon will be full) for each month and calculate the rest of each lunar cycle/month from there. It is a tricky business to get the twelve cycles of the Moon to work out to be the same amount of time the Earth orbits the Sun.

Egyptian calendar

An Egyptian man plows a furrow so the lady can sow seeds into it.

Both the Sumerians and Egyptians had economies that depended on agriculture—they grew crops for their food. If you ever planted tomatoes—or onions, or zucchini, or those two-ton pumpkins you see at the state fair—in a garden, you’ll have seen on the seed packages instructions about when to plant. If you plant your tomatoes too late, the fruit will never ripen in time before the first frost. This is why calendars are so important.

The Egyptians’ planting schedule was built around their river, the Nile. Every year the Nile would flood. After the floodwater receded, it left behind nutrient-rich silt that improved the soil. Egyptian farmers had to plant crops as soon as the Nile receded so they could harvest before the Nile flooded again.

By around 2450 bc the Egyptians had developed a calendar whose year was twelve months. Each month was thirty days long (12 x 30 = 360 days). The year was divided into three seasons—Inundation, when the Nile was flooded (Akhet), Emergence, time to plant the crops (Peret), and Harvest, time to gather the crops (Shemu)—of four months each, with five days added to the end of the year.

In case you hadn’t noticed, the Egyptian calendar used Base Sixty for counting the days. I’d like to think they sent a nice thank-you note to the Sumerians.

Base Sixty

Today we count using Base Ten (1-2-3-4-5-6-7-8-9-10, then 11-12-13-14-15-16-17-18-19-20, 21 to 30, 31 to 40, 41 to 50 and so on). Here’s something really interesting about the Sumerians. They counted numbers using Base Sixty! Fractions hadn’t been invented yet, so 60 was actually a handy base for counting. Sixty can be divided by 1, 2, 3, 4, 5, 6, 10, 12, 15, 20, 30, and 60. Try it!

Base Sixty is natural, it occurs in the world around us. By watching the sky, the Sumerians saw the Moon make a complete cycle 12 times a year. Each cycle (month) takes about 30 days (one day = the time it takes Earth to completely revolve around her axis). That’s about 360 days per year (one year = the time it takes Earth to travel around the Sun). These numbers fit neatly into the Base Sixty way of counting.

Do we still use Base Sixty? You betcha! A ruler is 12 inches long—12 x 5 = 60. We buy eggs and doughnuts by the dozen. Can you think of any other examples?

How about a clock? There are 12 hours on the face of an analogue clock—12 x 5 = 60. Sixty minutes in an hour; sixty seconds in a minute. What about 24 hours in the day—does that work? Nope, sixty doesn’t evenly divide by 24. But a protractor uses Base Sixty—a circle is divided into 360 degrees. If you were to mark 24 hours around a protractor, each hour would use 15 degrees (hang onto that thought—it will become important later on in the show).

I bought this one at Protractor Supply.

I can hear you saying, “Hold on, Manders. Years aren’t 360 days long. They’re 365 days and six hours!” Okay, I have to admit, that’s a good point. Sumerian astronomers were fantastic at math and did mostly everything right—but they got one really important piece of information wrong. They thought the Earth was the center of the universe with the Sun, Moon and planets revolving around her. It’s impossible to make the lunar year (12 cycles of the Moon) agree exactly with the solar year (Earth’s trip around the Sun), so we had to add 5 extra days, plus one day every fourth year, to make it work on a calendar. That’s not really the best solution, as we will see.