The Aztecs had a profound interest in astronomy and observed astral bodies very closely to track their movements. They were able to create an unusually complex and accurate calendar based on their knowledge of astronomy.
The calendar was also tied closely with Aztec symbolism and a specific symbol was assigned to each day. Each day was further associated with one of the four cardinal directions.
So the days and dates on the Aztec calendar not only had a literal significance but also carried a spiritual and mythological significance.
Aztec calendar cycles: The Aztec calendar comprised of two cycles. One was a 365-day solar cycle which the Aztecs called the Year Count. The other was a 260-day cycle which was called the Day Count. Together, these cycles aligned after every 52 years which the Aztecs called a century.
Aztec 365-day cycle: The Aztec calendar had 20 days in a month, so it counted 18 months. Since the calendar was tied to the solar cycle, it added up to a total of 365 days. Out of these, 360 days had a specific name.
Monthly celebrations: Each 20-day “month” began with celebrations at a festival. Moreover, symbols were ascribed to each of these 20-day periods in the 365-day cycle.
Unlucky days: The end of each 365-day cycle in the Aztec calendar was marked by 360 named days and 5 nameless days. The Aztecs considered these last five days as unlucky days.
260-day ritual cycle: The 260-day cycle on the Aztec calendar was called the ritual cycle. This cycle had immense religious significance for the Aztecs and they used it to mark different religious ceremonies and rituals. Priests also used this calendar to perform divination and predict future events.
Divisions of 260-day cycle: This cycle was divided into twenty periods of 13 days each. In a way, it comprised of a 13-day weeks. Each week in this cycle was associated with a specific Aztec deity. The second week, for instance, was associated with Quetzalcoatl, one of chief Aztec deities.
The Sun-stone: A stone-carved Aztec calendar, called Sun Stone, was recovered from the Aztec Empire and is extant. This calendar provides a detailed conception of the Aztec notions of time and space. The Sun Stone is divided into five portions, or five eras which are associated with five different Suns. This is in compliance with the Aztec mythology which says that mankind has perished at the end of four previous Sun cycles and that we are currently living in the fifth cycle of the Sun.
Sun Stone symbolism: At the centre of the Aztec Sun stone is the Sun god, Tonatiuh. He is shown with his tongue drawn out as a knife, to show that he required sacrifice. Tonatiuh is immediately surrounded by four symbols on the Sun Stone. Each of these symbols represent the previous four Eras of the Sun, as believed in Aztec mythology.
52-year cycle: Cycles are a prominent feature of Aztec mythology as well as their notions about time and space. The Aztec calendar comprises of several cycles. Among these is the 52-year cycle which marks the end of the Year Count and Day Count. Aztecs believed that every new 52 year cycle starts at the same day. So they performed rituals and sacrifices to ensure that the transition from one cycle to another happened without any catastrophes.
Aztec Calendar signs: Aztecs used many interesting signs to denote different days. Most of these signs made use of animal symbolism. One of the days, for instance, was marked by Crocodile, another by the Serpent, yet others were denoted by Rabbit, Dog, Monkey, Jaguar and a whole range of other animals.
Four Directions: Every day in the Aztec calendar was also associated with one of the four cardinal directions. Apart from the animal or object symbol associated to each day, it was also associated with North, South, East or West. The 6th day in the Aztec calendar, for instance, was assigned the symbol of death and it was associated with the North. The 20th day on the calendar, which was the final day of the month, was represented by a flower and associated with the South.
End of the World: Unlike the Mayans, Aztecs did not make any definite predictions regarding the end of the world. However, they did believe that at the end of every 52-year cycle of their calendar, gods could decide to destroy the Earth. This prediction was based on the alignment of the Year Count on the Aztec Calendar with the Day Count. This was considered unusual and ominous by the Aztecs. This is why they offered sacrifices and performed rituals at end of each 52-year cycle, hoping to secure another 52 years.
New Fire Ceremony: At the end of the 52-year cycle, Aztecs performed the New Fire ceremony. This ceremony was performed during the last five days of the final year of the cycle. In these five days, Aztecs observed fasting, performed sacrifices, abstained from different acts and observed silence. During the final hours of the fifth day, a sacrifice was performed at the formerly-volcanic summit of a mountain near Tenochtitlan. At this time, all fires were extinguished among Aztec populations and they looked to the summit for a sign. When the stars aligned to mark the beginning of the next day, the priests lit a fire at the mountain and this marked the beginning of the new 52-year cycle.
End of the fifth Sun: As depicted on the Aztec calendar, the Aztec mythology states that we are living in the reign of the fifth Sun. And that this Sun will also end in destruction, like all previous Sun Eras. The end of this Sun, according to the Aztec calendar, will come as a result of earthquakes.
Corresponding modern dates: Over the years, researchers have tried to map the Aztec dates and the beginning and end of the years and cycles in terms of the Gregorian calendar. In light of these researches, it has been found out that February 23 marked the first day of the Aztec calendar. Correspondingly, the date of the Fire Ceremony was February 22, a day before the beginning of the New Year.