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Mars Calendar Project

Many students (and adults!) are unaware of the origin of our calendar system. The calendar we use today was developed in 525 AD. The previous calendar, developed by the Romans, used the founding of the city of Rome (some 1200 years earlier) as its “zero date”. A monk named Dionysius Exiguus proposed using the birth of Jesus Christ as the “zero date” of the calendar (although most historians agree Dionysius got the date of that event wrong by a few years). The calendar was adjusted by Pope Gregory XIII in 1582 to eliminate errors that had accumulated over the previous century. Gregory also ordered that only centuries not divisible by 400 would be leap years (therefore, for example, 2000 was a leap year, but 1900 was not). This “Gregorian calendar” has become the standard used the world over, though not everyone adopted it at the same time. Britain and her colonies did not adopt it until 1752 (skipping 11 days between 3 September and 14 September, and resetting the beginning of the year from 25 March to 1 January). Russia did not adapt the new calendar until 1917, so the October Revolution is now celebrated on 7 November.

Other than the day/night cycle, the most obvious cycle that can track the passage of time is the cycle of the phases of the moon. It should come as no surprise, therefore, that all early calendars (with the exception of the ancient Egyptian calendar) were lunar calendars. Even the word “month” derives from the word “moon”. Originally there were ten months: January (from Janus, a Roman god), February (from Februar, a Roman festival of purification), March (from Mars, a Roman god), April (from the Latin word aperire, 'to open'), (May from Maia, a Roman goddess), June (from Juno, a Roman goddess), and September, October, November, December (from the Latin words meaning seventh, eighth, ninth, and tenth, respectively). Later, Roman emperors Julius Caesar and Caesar Augustus invented months to honor themselves, giving us the months of July and August.

The days of our weeks are, with a few exceptions, named for Norse gods: Monday (named for the Moon), Tuesday (named for Tiu, an Anglo-Saxon god or Tyr, a Norse god), Wednesday (named for Woden or Odin, a Norse god), Thursday (named for Thor a Norse god), Friday (named for Freya, a Norse goddess), Saturday (named for Saturn, a Roman god), and Sunday (named for the Sun). Under this system, the days of the week belonged to the god for whom they were named. Monday was literally “Moon’s Day”, Thursday was “Thor’s Day”, etc. Not all calendars have weeks. Historically, weeks are strictly religious cycles – unlike days, months, and years, they have no ties to celestial events.

The Gregorian calendar is the most widely used calendar today, but it is not the only one in use, even now. Calendars of other cultures which are still in use today include the Jewish, Chinese, and Muslim calendars. All three are lunar calendars, based upon cycles of the Moon, though the Jewish calendar is a complex mix of lunar and solar cycles.

Grade Levels: K-12

Time Frame: 30-45 minutes


Students will learn how the physical and orbital characteristics of Mars are similar to and are different from those of the Earth. Additionally, students will gain insight into the history of time-keeping on Earth and how the various calendars of Earth have evolved.

Real World Application:
Students will be given a handout that contains some information about how Martian “time” differs from Earth “time” and will be asked to create a calendar that represents these differences. This project will help students begin to understand how our own calendars came into being.

National Science Education Standards:
Standard D: Earth in the Solar System

What You Do

Introduce the idea of calendars and the history behind them. Discuss with your students why we have the time divisions (days, weeks, months, seasons, and years) that we do. Have the students do research to discover the equivalent values for Mars (they are listed here for your reference, but let your students discover them for themselves). It is up to the students to decide if these same principles will work for Martian time, and come up with a way to incorporate them. Here are some facts about Earth and Mars in the Solar System.

Earth/Mars Facts:

  • Mars has a rotation rate such that one day or sol (Martian day) equals 24.6 hours, or 24 hours, 37 minutes. The Earth rotates once every 24 hours.
  • Mars orbits the Sun in 687 Earth days. The Earth orbits the Sun in 365.25 days
  • The rotational axis of Mars tilts towards the Sun at an angle of 25 degrees. Earth has a similar tilt of 23.5 degrees. This tilt causes seasons on both planets.
  • Mars has two moons. Phobos travels around the planet twice in one sol. Deimos travels around Mars once a sol. The Earth’s moon orbits the earth once every 28 days.

From this information, the groups will design the Martian calendar. It is important to take into account such questions as:

  • Are you going to have days/weeks/months for your calendar?
  • If you have weeks, how many days will you have per week? What will the names of the days of the week be?
  • If you have months, how many days will you have per month? What will the names of the months be?
  • When will your New Year occur?
  • Will “leap years” be necessary? How will you handle “leap years”? Into which month/months will you put the extra days?
  • Do you think it will be necessary to coordinate with Earth holidays?
  • When is your “zero year” to be determined? We have established AD (also called “CE” or “Common Era”) on Earth.
  • How did you come up with the names? Do they have meaning?


Have the student groups present their calendars to the class. Depending upon your focus, you could evaluate the calendars (for utility or design), the names assigned to days, weeks, or months (for historical significance or other appropriateness), or on the accuracy of their calculations and conversions between Earth and Mars time. The quality of the presentation could be factored in as well.

  • For K - 5, a creative project would be to draw a calendar for one Martian year.
  • For 6 - 12, a creative project would be a paper or PowerPoint© presentation that describes their calendar in full detail. Research on the origins of Earth’s calendars would be appropriate prior to the start of creating Martian calendars.

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  What You Need
  • Encyclopedia, Internet, or other research materials

Optional Materials:

  • PowerPoint© for presentations
  • Calculators
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  • Maestro, Betsy. (1999). The story of clocks and calendars: Marking a millennium. New York, NY: Lothrop, Lee, & Shepard Books.
  • Sol
  • Axial tilt
  • Gregorian calendar
  • Phobos
  • Deimos

Space Studies 200 class at the University of North Dakota’s Mars Calendar Project
Adapted by ASU Mars Education Program
Mars Space Flight Facility
Arizona State University
(480) 965-1788