What Day Is It, Really? The Julian and Gregorian Calendars

What Day Is It, Really? The Julian and Gregorian Calendars
Martha Jefferson: Science, Medicine, Inventions and tech

Skill: Middle School
Time Required: One week


On Wednesday, September 2, 1752, Martha Wayles (and all British and colonial subjects) went to sleep as usual, and woke up 12 days later, on Thursday, September 14, 1752.  She was probably not surprised, because the British Calendar Act of 1751 had decreed this change the year before, and the citizens were prepared.  But one cannot help but think they must have thought it odd!


Students who participate in this lesson will learn the difference between the Julian and Gregorian calendars, the reasons for changing from one to the other, and other interesting facts about time and the calendar.

Materials Required:

Access to the Internet; paper and pen or pencil; art supplies.



1.  Introduce this lesson by asking student what day it is: when they answer, ask them if they are sure that is the case.  Suggest that it might, perhaps, be 11 days later.  At least, that is what happened once in our history!
2.  Explain the terms Julian and Gregorian with respect to calendars.  Then, divide the class into six groups, and using the web sites listed below, assign each group the following task:

               Group 1: How were the months of the year named? By whom?
               Group 2: How were the days of the week named?  By whom?
               Group 3. What is the history of the Julian calendar?
               Group 4: What is the history of the Gregorian calendar?
               Group 5: What are the strengths and weakness of each calendar?
               Group 6: What is at least one criticism of the Gregorian calendar?

3.  When the research is completed, ask each group to prepare a poster that will demonstrate its findings, and share it with the whole class.  Mount the posters around the classroom.
4.  Conclude the lesson with a discussion of what might be missed if 11 days were taken out of our calendar. Use some of the following examples and discussion starters: 

  • What if we went from December 17th to December 28th?
  • What if we went from July 1st to July 12th?
  • What if we went from February 3rd to February 14th?

Extending the Lesson:

This lesson might be extended by inviting an astronomy teacher or professor to talk with the class about the relation of astronomy to the calendar.

Sources & Resources:


The Julian Calendar

The Gregorian Calendar

The Curious History of the Gregorian Calendar

The British Calendar Act of 1751

Naming the Days of the Week

How Britain Got the Calendar Wrong


This lesson was developed by Averil McClelland, Kent State University.