A Brief History of the Calendar

I surprisingly often hear teenage atheists complain about what they perceive to be threats to their secular-ness, and one things I hear over and over is the ironic proposal of the argument: 'Well, Thursday is 'Thor's-day', so why don't we celebrate that?' This has lead me to believe that people are incredibly interested in the geneses and nomenclature of the current calendar. This strikes me as not only interesting, but something people may want to know, so, briefly, let's discuss that.
(the second half of this entry is a listing of name geneses, so scroll on down if you don't care about the history of the modern calendar)

The Briefest History of the Modern Calendar

The history of the calendar is very diverse, and to examine every root of the topic we would need to travel back thousands of years and to every far-flung corner of the planet. The Sumerians and Greeks both had 12-month calendars, and the Mayans and other Mesoamericans had complex, two-year calendars. Because of the etymology involved, however, I will be looking only at the Roman calendar, and this is the one that would ultimately become the one we use today, to say nothing of its own history.

According to the Romans, their calendar was founded, like everything else, by Romulus around the time of Rome's own founding, around 753 BC, the supposed date that Rome was born. This calendar consisted of ten months, the first few named after a pretty diverse collection of gods like Juno and Mars (Roman), and Aphrodite and Maia (Greek), with some Etruscan influence in the nomenclature. The last few months, Quintilus through December, translate from the Latin to mean fifth through tenth - which makes sense, I guess.

Romulus' calendar got an update around 713 BC, when a Roman King named Numa Pompilius added two months, Ianuarius and Februarius, the former named after the Roman god Janus, and the latter after the purification ceremony of Februa held in that month.

The last real update that the Romans performed came by, who else, Julius Caesar. Serving as Pontificus Maximus (high priest) in 63 BC, Caesar made a number of changes to the calendar unimportant to our purposes here, but what is more important is the final act of his reforms, carried out by his nephew and adopted heir, Augustus. Augustus renamed the first two yet-unnamed months (the seventh and eighth months, still named 'fifth' and 'sixth') after the great Caesar and himself, giving us July and August.

Pope Gregory XIII

The most important revision of the calendar was the institution of the still-used Gregorian calendar. The 325 AD Council of Nicaea (one of the most important events in Christian history, for those interested) outlined when Easter should take place. For a number of reasons, although the Council had decided Easter should be celebrated simultaneously throughout the Christian world, it was not. Additionally, because of small errors binding the lunar cycle to the Julian calendar, by the 16th century Easter was out of whack by four days.

The solution was the modern calendar involving leap years and years without leap years (every hundredth year is not a leap year, but every fourth hundredth year is a leap year, simple stuff like that), instituted in 1562 by Pope Gregory XIII, who gave the calendar its name. This included a ten-day reset for the calendar in February of that year, and now we have the entire planet on a standardized, unwavering calendar that stays true to the lunar cycles. It's cool stuff if you know what you're talking about. Or, I would assume it is.

TL;DR - The Names of the Months

January - Named for Janus, the Roman god of gates, doorways, beginnings, and endings. This is appropriate for the month containing the rebirth of the year.
 
February - From the Latin Februalia, a holiday of purification occurring during the full moon of the second month (13th-15th). The ceremony could date back to the pre-Roman Sabines, and relate to the raininess ('washing away') that comes with that part of the year in Italy.
 
March - Originally Martius after the Roman god of war, Mars. In the Mediterranean, the third month marks the spring thaw, and with it, the beginning of campaign season. In ancient times, armies marched (that's right) in seasons. When the snows came, the armies 'wintered' until the next thaw, when they could march (yes) again.
 
April - The nomenclature on this one is a little suspect, and you have to reach a bit. One option is that it comes from the Latin aperire, 'to open,' referring to the budding of trees and flowers. This works well with the Greek anoixis, which means both 'opening' and 'spring.' Given the Romans' penchant for stealing nomenclature from the Greeks, this makes the most sense, though some have also suggested it may come from the Greek goddess Aphrodite, called in Greek Aphros, referred to in Latin as 'Aphrilis' and in Etruscan as 'Apru.' Given that April was holy to the Roman goddess Venus (the equivalent to Aphrodite) and contained her festival, the Festum Veneris et Fortunae Virilis, either option seems to make sense.
 
May - From the Greek goddess of nature, Maia. For reasons similar to the reckoning of aperire. Maia was the goddess of nature and fertility, and her month marked the rebirth of nature for the coming summer.
 
June - For the Roman goddess Juno, wife of Jupiter. She was kind of famous for being married to the king of the gods, so her month was a popular one for young couples to be married.
 
July - The birth-month of Julius Caesar, Augustus picked this month to forever recall that great man.
 
August - Similarly, Augustus selected this month to bear his name. Despite many common myths stating otherwise, Augustus (according to Macrobius) chose August because many of his greatest triumphs occurred in that month, including the taking of Alexandria.
 
September, October, November, and December - All translate from the Latin meaning 'Seventh, Eighth, Ninth, and Tenth.' This is en excellent lesson on the impact of Latin on Western language. If you speak French, German, Dutch, Portuguese, Spanish, or Italian, you should recognize several of these terms. For instance, sept is French for 'seven', acht is German for eight, nove means 'nine' in Portuguese, and decimo means 'ten' in both Spanish and Italian.