Byrdseed

Photo by lydia shining brightly

We’ve just experienced the solar new year, and now many cultures will celebrate the lunar new year.

Looking at calendars throughout history is an interesting way to explore multiple perspectives. Nothing is as ingrained in our lives as seven day weeks, twelve months, and 365 days per year. Challenge your students’ perceptions by investigating various solar, lunar, and lunisolar calendars.

Solar vs Lunar

Begin by exploring the advantages of a solar calendar and a lunar calendar.

A solar year occurs once every 365 days, 5 hours 49 minutes 19 second (or about 365.242 days). The Gregorian calendar, the internationally accepted calendar, follows a solar year and your students should be familiar with the Earth’s annual trip around the sun.

Meanwhile, a lunar calendar follows lunar cycles, which average 29.530589 days (thank you Wikipedia). Twelve of these cycles result in a lunar year that’s about 354.37 days long.

The Islamic calendar is a pure lunar calendar of twelve months.

Lunisolar

However, very few cultures have used a true lunar calendar, instead opting for a combo lunisolar calendar.

For example, the Egyptians followed a calendar of twelve lunar months, each with thirty days. Since this only equals 360 days, they added five more days at the end to line up with the solar year.

Adding extra days to connect lunar and solar calendars is common across many cultures. These days are known as intercalary days.

The Aztecs had a calendar which lasted for eighteen, twenty day periods, plus five extra days known as “nameless days” or nemontemi.

Non-Standard Years

Not everyone used a 365 day year. Various Mesoamerican cultures used a 260-day “ritual” calendar that had no relation to the sun, moon, or seasons.

Weeks and Days

We take our seven day week for granted, but there have been a variety of week lengths throughout history.

The Egyptians used a ten day week. There were exactly three weeks in their thirty day months. The French calendar also used ten day weeks during the French Revolution.

China also had periods where they used ten day weeks.

The Romans used an eight day week, with days named A though H.

The Soviet Union went with five day weeks, labeled with colors or Roman numerals. This only lasted a couple years before they moved onto six day weeks, and then, eventually, the seven day week.

Create

So what on earth can we do with all of this information?

This might fit into a calendar-creation activity. I have my students design their own civilizations, to connect with our study of ancient civilizations.

I would ask them these questions about their civilization’s calendar system:

1. How many months will you have?
2. How many days will be in each month?
3. Will this equal 365 exactly, or will you use intercalery days?
4. What will your months be named?
5. What will your days be called?
6. Explain the the significance of the names of your months and days.

Going Further

The various calendar systems are fascinating and could turn into an independent study for interested students.

Social Studies

• Study the origins of the Gregorian calendar.
• Explore the transition from the Julian to Gregorian calendar.
• Examine the popularity of certain calendars in geographical regions.
• Investigate the influence of various religions on calendars.
• Digging into the month’s names opens up interesting avenues, and connects with Ancient Roman history (Simple Wikipedia is a student-friendly resource for this).
• Learn other language’s names for the days and months.

Math

• Investigate the combinations of months and days that equal 365. For example, ten 36 day months gets us to 360.
• Add in weeks to the previous idea and try to make everything a nice, round number. How many options are there?
• Determine how many 354 day lunar years it takes to line back up with 365 day solar years. How many 260 day years?

Science

• Develop calendars for different planets in the solar system (Jupiter’s solar year consists of 10,475.8 Jovian days).
• Explore the seasons’ impact on calendars (Rome considered winter a monthless period!)

Please let me know if you come up with a great idea using calendars.