How to setup a Julian calendar

Aeon Timeline lets you customize your calendar, including configuring a timeline to use the Julian calendar.

Note: Calendars can only be edited when there are no items or calendar markers included in the timeline. Once your timeline contains items with dates, editing will be restricted to renaming components such as months and weekdays.

How does the Julian Calendar differ from the Gregorian Calendar?

The Julian calendar is very similar to the modern Gregorian calendar, but it uses a simplified leap year model:

Calendar Leap Years
  • Every 4 years
  • Every 4 years
  • Except every 100 years
  • But including every 400 years

This change in the leap year model was introduced to prevent the drift that occured with the less accurate Julian model (it is all based on the average length of a year not being a whole number of days).

How to configure a Julian Calendar

To convert the Gregorian calendar into a Julian calendar, we have to do two things:

  1. Adjust the leap year model to the simplified calculation
  2. Align the weekdays to the dates correctly

Begin editing the calendar

  1. Create a new timeline using any of our standard templates that use absolute dates
  2. Open Timeline Settings, and then click Edit Calendar

Adjust the leap year calculations

The leap years need to be adjusted to be every 4 years, rather than the more elaborate Gregorian approach:

  1. Click onto the Eras tab
  2. Click on Customize leap years
  3. Erase the last two text fields, leaving only the top field with a number
    • Due to a current bug, you cannot actually erase the fields by deleting the value. But if you type a value that is not a multiple of 4 into the 2nd box (e.g. 10), they will magically delete for you. We will fix this problem soon so you can delete them in a more sensible manner!

Adjust the weekdays:

To align the weekdays to dates correctly, we need to tell Aeon Timeline which weekday should be used as the "first weekday of final era": that is, what was the weekday for 1 January 1AD.

In the Julian calendar, that day was a Saturday.

To set this correctly:

  1. Click onto the Weekdays tab
  2. In the top section, choose Saturday as the First Weekday of Final Era

Save the calendar and test

To save your changes:

  1. Click OK on the Edit Calendar window
  2. Click OK on the Settings window

Your timeline will now be adjusted to use the Julian calendar.

It is a good idea to test the calendar is behaving as expected by comparing it to another Julian date calculation source that you trust.

The image below shows:

  1. Two events created 3500 days apart (using a Date Constraint to ensure they are the correct distance).
  2. An inlay shows a Julian date calculator specifying the same 3500 day gap, and the same weekdays for both events.

Comparison source: