Happy New Year!

I hope you all enjoyed the holidays and got well into the new year. Since my last post I’ve been trying to round up some parts of the web application to make the service ready for use. In addition, I started testing the application. These two subjects will be the focus of this post.

Rounding up

I’ve removed, the features and drop-down forms with different abilities to determine dates. So, for now, just a year shall be entered in the search box. I still hope to introduce features to assist in determining a date from whatever text can be read from a church book, to convert a date from one calendar to another, and to determine a date from another date and an age. However, for now I’d like to get the calendar wrapped up and see if somebody will actually start to use it. Similar, I ended up with Julian, Gregorian and Danish calendars. It is still my ambition to add other Nordic calendars and maybe other European calendars later.

I had a wish to add some information in the application about years and named days - like when some named day has been changed or has been removed from the calendar by law. Another idea I had was to show a year in the way that the church or a state or other entity might have considered it. For instance starting from the first Sunday in Advent in the “previous” year. A third idea was to include different views, for instance, a full calendar or just a listing of named days. These are all still potential future features.

Finally, I’ve added a short welcome message when no year has been entered and no calendar is shown. I considered showing the current year or some more elaborate text about how to use the calendar in relation to determining dates from church books or similar. But for now I settled on a short welcome message with a short description on how to use the application.


As part of rounding up the calendar application and making it ready for use, I’ve also added some automatic testing of the calculations. Currently I test the years from the different calendars for whether they have the right days in each month, if the weekdays are correct and finally whether Easter and a few other named days are calculated correct. I originally did not have R. W. Bauer’s book with me, so I checked against some of the other calendar services out there. Generally, the services seemed to agree, but I did come across a couple of issues, which I will elaborate in the following.

Leap year in the Gregorian calendar

The calendar service I primarily tested against has 1700 and 1900 as leap years. And for other years 1800, 2100 and 2200 it has notes in the top indicating that one should be aware that these years were not considered leap years according to R. W. Bauer. This makes me think that perhaps some confusion about the leap year rule had led to some incorrect adjustments. Bauer’s calendar variants were done in such a way that the leap year variations matched the non-leap year versions except in January and February. Incorrectly, using the non-leap year variations only renders January and February incorrect. For 1700 it is indicated that the shown calendar can only be used from March and forth, as Denmark was using the Julian calendar before March 1700. In this way, it is actually only the two month in 1900 that are a bit incorrect.

The Gregorian calendar introduced a change to the leap year rule, as the Julian calendar’s average year was longer than the actual time it takes our planet to travel around the sun. The Gregorian calendar removes three leap years in 400 years, by leaving out those years that are divisable with 100, but not 400. That means that 1700, 1800, 1900 are not leap years in the Gregorian calendar while 1600 and 2000 are leap years.

The year 1744

The calendar service I primarily tested against differed from my calendar one other year; 1744. Here our calendars agreed that the year is a leap year and starts on a Wednesday and ends on a Thursday. But they disagree by a week on when Easter falls. As I didn’t have R. W. Bauer’s calendar available at first I compared with other services. I found that morchslaegt.dk, rmadsen.dk, dinslægt.dk and Familysearch wiki all agreed that Easter Sunday falls on March 29 while my calendar wants it to fall one week later on April 5. Accordingly there is one week difference between many of the church days of 1744 in these services and my calendar as they fall relative to Easter.

I’ve tried two different algorithms for determining Easter from Wikipedia and they both determine Easter to fall on April 5. I have also since gotten my hands on R. W. Bauer’s calendar again and have looked up the year 1744. Under the new style or Gregorian calendar it indicates that calendar 15 (in the leap year variation) shall be used. Checking calendar 15 I see Easter fall on April 5. The morchslaegt.dk calendar indicates it is based on Bauer’s work and for some reason it is using Bauer’s calendar 8 (leap-year variation) for 1744 rather than calendar 15. This could just be an error when entering all the data. However, it seems unlikely that all the different calendar services have made a similar mistakes or that all somehow are based on the same data with the error in it.

Until next time

I will try to write to some of the different calendar services to understand if they are wrong about 1744 or if there is something that I’m not aware of in my calculations. I will also try to go through the individual church days in the calendar and settle on which ones to include and whether to have different rules or introduce and remove some over time as I did for “Mariæ Bebudelse” (Annunciation) that has changed over time in Denmark.

I have already started and will continue to blog less frequently - aiming at around once a month. It is hard to find time for this side project and I want to strike a balance between working on the application and blogging about it.

Happy New Year,
Morten Olsen