Dozenal Calendar

If you've ever thought about the etymology of the names of the months, you may have noticed an interesting pattern. In our Gregorian Calendar, the last four months have numerical prefixes.
September
October
November
December
These are Latin prefixes meaning "seventh", "eighth", "ninth", and "tenth", respectively. Unfortunately, these are not the seventh, eighth, ninth, and tenth months. Like with many everyday concepts, the reason for this goes back to the Roman Empire. The ancient Roman Calendar had 10 months. They started naming the months after deities, but it seems they ran out of ideas after Juno. The Romans loved the number ten, so they used numerical month names for the remaining months.
Roman Month Meaning
Martius Mars
Aprilis Aphrodite
Maius Maia
Iunius Juno
Quintilis Fifth
Sextilis Sixth
September Seventh
October Eighth
November Ninth
December Tenth
As Rome grew and changed, they updated the calendar by adding, renaming, and reordering the months. They ended up with the Julian Calendar, which later became the basis for our modern Gregorian Calendar. The once descriptive naming of the seventh through tenth months is now just a traditional naming convention.

After learning this, I felt the need to fix it. So I designed a calendar that has a more organized naming convention, and more uniformly distributed days. Of course I don't expect it to challenge the well-established Gregorian Calendar. But it was an enjoyable world-building excercise that may be useful in works of science fiction.

First, I decided that all months should have the same number of days. No more of this "Thirty days has September" nonsense. I love the number twelve, so I kept the twelve month format. The problem is, twelve does not divide nicely into 365 days. Every month would need to have 30.416 days. That's pretty close though. If I round down to 30 days per month, it only leaves 5 days left over. We'll get back to those.

The whole concept of a year is based on the movement of the sun. Some calendars follow the moon, but most calendars are built around the movement of the sun across the sky and the changing in the length of a day.
Significance Fixed Point Gregorian Date
Shortest DayWinter SolsticeDecember 21st
MidpointSpring EquinoxMarch 21st
Longest DaySummer SolsticeJune 21st
MidpointFall EquinoxSeptember 21st
These are pretty concrete times of year so I decided to base my calendar directly on these days. My year would start and end on the Winter Solstice and the months would be distributed evenly around those fixed points. On the summer solstice, exactly six months should have gone by. It was at this point in the process that I began to form a solution for my 5 leftover days. I decided to assign one of the spare days to each fixed point. This means that the solstices and the equinoxes are not considered part of any month. That took care of all but one extra day, plus leap day. In the interest of distributing the days as evenly as possible, I placed the extra day on New Years Day, the day after Winter Solstice, and placed the leap day immediately after Summer Solstice, on the opposite side of the year.
New Year's Day
Month 1
Month 2
Month 3
Spring Equinox
Month 4
Month 5
Month 6
Summer Solstice
Month 7
Month 8
Month 9
Fall Equinox
Month 10
Month 11
Month 12
Winter Solstice
This layout made me very happy. At month 4, it is clear that we are one third through the year. Every month has 30 days so there's no need for memorizing arbitrary numbers. The external days are closely tied to the length of the day and therefore make intuitive sense.

The only thing left was to name the months. I didn't want to revive the Roman numerical naming, since it might be confusing to differentiate between my 30-day November and the old 31-day November, especially since they don't line up nicely. So I scrapped the old names and went searching for something new. I could have done numerical names in a different language, such as Greek, but that seemed to uninspired to me. In any case, the months didn't have to be descriptive, just consistent. All I really needed was a set of twelve familiar words to identify the months. Ideally it would be something connected with the sun and the sky. And then it hit me.

The oldest way of telling the time of year was to observe the positions of the constellations. As Earth rotates throughout the day it quickly sweeps out a view of the sky. Over the course of a day, the sun and moon appear to be fixed against the background stars. Over the course of a year, the sun appears to move across the constellations in a great circle. Ancient peoples learned which constellations were in the sun's path and they would characterize a time of year by which constellation the sun was currently inhabiting. This was how they knew the best time to plant or harvest crops. The cycle of constellations in the sun's path is called the Zodiac. And there are twelve of them.

So I named my months after the zodiac constellations. They were already on a natural year long cycle divided into twelve pieces. I just named each month after the constellation that was most prevalent during that time.
New Year's Day
Sagittarius
Capricorn
Aquarius
Spring Equinox
Pisces
Aries
Taurus
Summer Solstice
(Leap Day)
Gemini
Cancer
Leo
Fall Equinox
Virgo
Libra
Scorpio
Winter Solstice
To take it a step further, I also redesigned the week. The traditional seven-day week would not fit neatly into 30 days. I don't care for the number seven anyway, I like composite numbers like 12 and 6. So I designed a new 6-day week and made each month 5 weeks long. Again, I decided to throw out the old day names to avoid confusion. But I liked how the days of the week are derived from the traditional seven celestial objects. Our modern names come mainly from the corresponding Norse Gods, but it goes back to the Greeks. So I started with the Greek Gods and anglicized them a bit.
Day Celestial Body
/Roman God		 Greek God New Name
Sunday Sun Helios Heliday
Monday Moon Luna Loonday
Tuesday Mars Ares Ariday
Wednesday Mercury Hermes Hermiday
Thursday Jupiter Zeus Zuday
Friday Venus Aphrodite Afriday
Saturday Saturn Kronos Croneday
But to make it six days, I had to remove one. Since my calendar is already based on the sun, I figured Sol was getting enough representation and decided to remove Heliday. Now the six-day week begins with the day of the Moon and ends with Cronus, the titan of harvest who led the first generation of titans.

With this neatly organized week, the day of the month now falls on the same day of the week every month in every year! The 1st is always a Loonday, the 9th is always a Hermiday, regardless of month.