Ancient Numbers, Dates, and Calendars
Activity: Students will learn about number systems and calendars
of the ancient world. While different from ours, these early number systems
were just as sophisticated. First, students will look at the ancient Maya
number system and try a few math problems. Then they'll learn how the
Maya counted days and years and explore the Aztec calendar system with
its special symbols for particular days, months, and years. Finally, they'll
study different images from the Sun Stone, a famous Aztec artifact.
Background: Though most ancient cultures supported themselves through
farming, large urban areas were beginning to develop that served as religious,
cultural, and economic centers. One example is Teotihuacán, a city named
for the early Central American people who built it. The city was so impressive
it was used by a later society, the Aztec, as a sacred place for worship.
Another ancient city, Chichén Itzá, was built by the Maya on the Yucatán
Peninsula. Both ancient cities are known for their unique pyramids.
 Visit the Maya Mathematical System site (below) to explore the number
system of this ancient civilization. For example, the Maya did not count
by using the numbers 1, 2, and 3. Instead, their system used three symbols:
the dot (representing one unit); a straight line (representing five
units); and a shell (representing zero). Have students draw the symbols
that represent the numbers 1 through 20.
 The Maya number system is based on 20 units. Ask students how many
units our decimal system is based on. (The answer is 10. We understand
numbers in multiples of 10.)
 Use the Maya numbers to write a few simple math problems on the board
and challenge students to try to answer the problems using Maya numbers.
For younger students, be sure the numbers in your problem and the answer
are equal to or less than 20.
 Explain that the Maya also used a different calendar from ours.
But like ours, the Maya calendar was based closely on the movement
of the Earth and sun. Share these basic facts:
 A day was called a "kin." The Maya calendar has a cycle
of 20 days
 The Maya year is divided into 19 months or "uinals."
(Each uinal has 20 days, except for the last one of the year, which
has five.)
 The Maya year, or "tun," was 360 days, very close to
the number of days in our year.
 The Maya used unique glyphs, or symbols, to represent each day
and each month.
 Maya used these glyphs combined with numbers to write dates. Important
dates were carved in stone monuments called "stelae."
 Go to the site "Maya Calendar: The Components" (below) to see the
glyphs used to represent different days and months. Have students click
the link at the bottom of the page to see a stela with today's date.
 Explain that another ancient culture, the Aztec, also had its own
ways of recording and measuring time. Like the Maya calendar, it used
symbols and numbers to express the different days, cycles (months),
and years. Share these basic facts with students:
 The Aztec actually used two calendars. One related
to the seasons and had 365 days like ours. It was used to decide
when to plant crops. The second calendar was sacred and had 260
days. This religious calendar told when rituals would take place
and when to consult the gods.
 Like the Maya calendar, there were 20 days in a cycle, each with
a different symbol or day sign. Every day sign is dedicated to a
god.
 The Aztec year was divided into 13day periods. Like the days,
each year and 13day period had their own symbols dedicated to a
different god.
 Since different days belonged to different gods; each day could
be good or bad, depending on the god of that day. For example, a
day dedicated to the god of pleasure, is a good day to be lighthearted.
 The Aztec could express the date using the symbols and numbers. Go
to "Aztec Calendar" (below) to see today's date. Click on the day sign
(the third symbol) to find out which god owns the day. What is it a
good day for? Students may also want to type in their birthdays to see
the date in Aztec.
 Finally, tell your students about a famous Aztec artifact. The Aztec
Calendar or Sun Stone, a 12foot rock, was carved in 1479 and dedicated
to the principal Aztec god, the Sun. Show students the image at the
site "The Aztec Calendar: Sun Stone" (below).
 In the center of this round calendar is the face of the sun, the
"Lord of Heaven." Each ring surrounding his face symbolizes different
periods, days, or natural occurrences.
 Print out the image of the Sun Stone. Divide the class into four
groups and assign each group one of the following: First Ring, Second
Ring, Third Ring, or Outer Ring.
 Within each group, have students choose one symbol to learn about.
Have each student recreate the symbol and write a brief description
of its meaning on a 4by6inch index card.
 Display the printout of the Sun Stone on your bulletin board. Have
students post their cards around the Sun Stone, connecting their cards
to the related part of the Sun Stone image.
