Our Gregorian Calendar—which has more or less succeeded in its primary objective of keeping in phase with seasons—has received a great deal of criticism. Many organizational problems are caused, both in scheduling and period to period comparisons, because its calendar months, quarters and years all begin on various days of the week. As a result, most annual events experience a change in either day of the week or date in the month from one year to the next.
Many people have advocated the use of a perennial calendar (one that is the same every year) to overcome this situation. But changing to a good perennial calendar has its own problems. That’s because solar year length is just over 365.24 days. Some method of dealing with that uneven number would be necessary in order for each yearly event to always occur on both the same day of the week and date of the month in all years, common and intercalary.
Calendar designers have resorted to various means, some of which appear to be more successful than others in working around the year’s uneven number of days. Here are some techniques used, together with links to calendar designs incorporating them:
- Add a 13th month – Bonavian Leap-Month and Cotsworth.
- Two days are not part of any week or month – World and Tolkein’s Shire.
- Extend some day lengths (beyond 24 hours) – Long-Sabbath.
- Intercalary weeks – New Millennium.
- Two different week lengths – Fixed-Week
All of the above types of calendar modification have both advantages and disadvantages over each of the other kinds. If you would like to compare their features you should view A Perennial Calendar Comparison.