All different civilisations and/or cultures have their own calendar. I can confidently tell you that today is July 16th, 2010, because I'm using the Gregorian calendar. The Maya could equally confidently tell you that today is 12 B'atz' 4 Xul. A Jew would be absolutely certain that today is 5 Av, 5770; while the Chinese are just as sure that it's 5 Liù Yuè, in the Year of the Tiger. We're all right, but sometimes these calendars can't just be superimposed onto each other, as we might not be using the same calculations to get to the date.
The Gregorian calendar, with its date of July 16th, 2010, is based on a solar year. It takes, approximately, 365 days for our planet to travel around the sun. However, this reckoning isn't precise. We don't travel around the sun in a perfect circle. It's more a sort of oval, though this can also change gradually over time.
It actually takes the Earth a fraction longer than 365 days to make that progress. In fact, it's more like 365.22 days. This can be a problem when you're trying to use it to count your days. In the Gregorian calendar, we have a Leap Year, every four years, to correct our count. This gives us 366 days in a year every 4th year, while the intervening 3 only have 365 days. On that 4th year, our Christmas Day would be celebrated on December 26th, as reckoned by the previous three years.
The Maya also looked to the sky to form their calculations of the date. However, they had worked out, long before the rest of Western civilisation, that the calendar count had to take into consideration the real progress of the Earth around the sun. Their solution was to have not one, but three calendars, with mini-cycles within them. They all interlinked, but counted different things.
The most important calendar for the Maya is the Tzolk'in, which lasts for 260 days. The end of the Tzolk'in is New Year for the Maya, hence the actual date of it moves around the Gregorian calendar, which is longer.
The Tzolk'in is equally divided into 20 trecena. This counts just 13 days and was used by both the Maya and the Aztec. The trecena notes each day with the simple number - 1 to 13, then starts again.
There are also 20 day names, which run alongside the numbers of the trecena. These are: B'atz', Ee, Aj, I'x, Tz'ikin, Ajmaq, No'j, Tijax, Kawoq, Ajpu, Imox, Iq', Aq'ab'al, K'at, Kan, Kame, Kej, Q'anil, Toj and Tz'i'. The date would be this day name alongside the number on the trecena. So day one is B'atz' 1; day two is Ee 2 etc. This is straightforward until you reach the 14th day, when you run out of trecena numbers. You just start again on the trecena count. So day 13 is Aq'ab'al 13; and day 14 is K'at 1. Day 20 is Tz'i' 7; while day 21 is B'atz' 8, as we've started again with the first of the day names now.
While this looks more complicated than all that we're used to with our Gregorian calendar, it's not really. Right now, July 16th is Friday, but it doesn't follow that every 16th day of the month is a Friday. We shuffle seven day names between up to 31 numbered days; the Maya shuffle twenty day names between 13 numbered days. That's all. The beauty of the Maya way is that, when combined with a Haab' calendar year, it takes 52 years for the same combination of number and day name to swing back around. For the ancient Maya, that was longer than life expectancy, so they'd probably never see it again. Every day of their lives, therefore, had its own unique label.
But why 260 days? The Maya didn't just look at the sun. They also factored in the Tropical Year, as well as the passage of the moon, Venus, Mars and Jupiter. Once a lot of complex mathematics have passed, we are left with a calendar accurate to within 0.07 days per 100 years. For more on this theory, please visit The Mayan Calendar - Why 260 Days?. Others have argued that there's a more earthly reason. 260 days is the time that passes between a woman's first missed period and the birth of her baby.
The second major Maya calendar is the Haab', which runs from Winter Solstice to Winter Solstice. This one will feel far more familiar to those of us used to the Gregorian calendar, as it lasts for 365 days. It's split up into 18 months, each with 20 days in them, along with a 5 'nameless day' period. As with the Gregorian calendar, it is far less accurate than the 260 day Tzolk'in, because it loses time every year.
The names of these months are: Pop, Wo, Sip, Sotz', Sek, Xul, Yaxk'in, Mol, Ch'en, Yax, Sac, Keh, Mak, K'ank'in, Muwan, Pax, K'ayab', Kumk'u and Wayeb'. Each would have the number of the day before them, starting with 0 and ending with 19. So day one is 0 Pop; day two is 1 Pop; all the way to 19 Pop, which is followed by 0 Wo. This sequence only changes slightly at the final month, which starts with 0 Wayeb', but finishes with 4 Wayeb'. The next day would be 0 Pop, as a new cycle begins.
This calendar allowed them to plan an agricultural year.
The Long Count
This is the Maya calendar that is so infamous in modern lore, in that it has been interpreted as predicting the end of the world in 2012. There's a whole new blog in that and so I will return to it on Monday.