The Symmetry010 Calendar

Created by Dr. Irv Bromberg, University of Toronto, Canada

[Click here to go back to the Symmetry454 / Kalendis home page]

Don’t be Anti-Symmetric!

Join the Calendars LISTSERV

Contents

• Call for Calendar Reform
• Overview
• Epoch
• Leap Rule
• Benefits
• Documentation

Call for Calendar Reform

The Gregorian calendar is deficient in the following ways:

• Each consecutive Gregorian year starts on a different weekday. This is the most serious deficiency of the Gregorian calendar. If it were impossible to correct this deficiency by adopting a perpetual (perennial) calendar reform then we wouldn’t care about the rest of this list. This deficiency causes the dates of holidays and events to shift. Those that fall on a fixed day number in a month fall on a different weekday. Those that fall on the n^th occurrence of a specified weekday in a month fall on a different day number. These shifts compel organizations such as governments, businesses, industries, and academic institutions to consume vast amounts of time, energy, and paper rescheduling annually recurring events just because of the changing weekday-date relationships. Even monthly recurring events are cumbersome to schedule. Easter can land on any date from March 22 through April 25, and numerous ecclesistical days counted before and after Easter wander likewise.
• The lengths of the Gregorian months follow an illogical, irregular pattern: 31, 28 or 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31 days.
• When dividing the Gregorian calendar year into 4 groups of 3 months the resulting quarters have unequal day counts and unequal ratios of workdays to weekend days.
• Appending the leap day at the end of February causes unfortunate calendrical complexity, because it increments the ordinal day number of every date following February in leap years. This problem could have been avoided by appending the leap day to the end of the year.
• The Gregorian calendar mean year is currently almost 12 seconds too long relative to its intended target, the mean northward equinoctial year (also imprecisely known as the spring or vernal equinox year).
• Given a Gregorian date, moderately complicated arithmetic is required to determine the weekday.
• The weekday occurrences of the leapdays in each full 400-year Gregorian leap cycle are unequal:
  Monday=15, Tuesday=13, Wednesday=15, Thursday=13, Friday=14, Saturday=14, and Sunday=13.
• Many people are superstitious about bad luck occurring on Friday the 13^th.

A perpetual calendar reform is of prime importance, starting every year on the same weekday while conserving the traditional 7-day sabbatical cycle. The following recent precedents support conserving the sabbatical cycle as an absolute requirement:

• The French Republican calendar was implemented during the French Revolution until Napoléon abolished it just over 12 years later, and again for only 18 days in 1871. Its perpetual calendar year began at the autumn equinox and had twelve 30-day months with three 10-day weeks per month, plus 5 national holidays at the end of the year (6 in leap years). Religious objections to its disruption of the 7-day sabbatical cycle and workers’ objections to 10-day weeks ultimately led to its downfall.
• The 13 Month calendar was a proposed perpetual calendar reform having thirteen 28-day months plus an extra day at the end of the year outside the 7-day sabbatical cycle. A month called Sol was inserted between June and July. Its leap day was inserted before Sol and was also outside the sabbatical cycle. Every month started on Sunday, so every month had a Friday the 13^th. The arithmetic for calendrical calculations was never published by any of the individuals or organizations who promoted it. The League of Nations rejected it in 1937 because of religious objections to its disruption of the 7-day sabbatical cycle, and because it wasn’t divisible into 4 equal quarters containing whole months.
• In 1929 USSR switched to a 5-day week with work schedules rotated to maintain continuous productivity, but that failed because family and friends had different days off work, and it was difficult to maintain equipment that was in continuous use. By 1932 they switched to a 6-day week with a common day off. In 1940 they reverted to the 7-day week, to increase productivity! (1 day off in 7 days is more productive than 1 in 6)
• The World calendar was a copyrighted proposed perpetual calendar reform having 4 equal quarters of 31+30+30 days each, plus Worldsday at the end of the year, outside the 7-day sabbatical cycle. In leap years Leapyear Day was inserted after the end of the second quarter and was also outside the sabbatical cycle. Every quarter started on Sunday, so the first month of each quarter contained a Friday the 13^th. The arithmetic for calendrical calculations was never published by any of the individuals or organizations who promoted it. The USA vetoed it at the United Nations in 1955 because of religious objections to its disruption of the 7-day sabbatical cycle.
• The International Organization for Standardization formally specified the 7-day week as the international standard in ISO 8601.

• to encourage standardized error-free implementation in computer systems and electronic devices
• to assist with conversions of pre-reform date records.

Minimal change isn’t important for calendar reform. Although it’s possible to make the Gregorian calendar perpetual without solving any other deficiencies (start every year on Saturday, February = 27 days in common years or = 34 days if the remainder of (71 × year + 200) / 400 is less than 71), when making any change we may as well solve every deficiency, to obtain an optimal outcome and enjoy all the benefits.

The Symmetry010 or its sister Symmetry454 calendar reform will solve all of the Gregorian calendar deficiencies.

The Symmetry010 calendar is a simple perpetual solar calendar that fully conserves the traditional 7-day week (by using a leap week instead of a leap day), has symmetrical equal quarters each having 30+31+30 days, and starts every quarter on Monday. The Symmetry010 calendar arithmetic is openly documented, royalty-free.

Overview of the Symmetry010 Calendar

The Symmetry010 calendar is a simple perpetual solar calendar that conserves the traditional 7-day week, has symmetrical equal quarters each having 30+31+30 days, and starts every quarter on Monday.

Holidays and special days, indicated with background yellow shading, are permanently fixed.
Hover over the day number to see the pop-up event description.
All Easter-related ecclesiastical calendar days are shown on the fixed dates that they would have if the proposed perpetually fixed Easter date of Sunday April 7^th were adopted (based on the median astronomical Easter date, and the fact that Julian Sunday April 9, 30 AD was Symmetry010 Sunday April 7, 30 AD).

First Quarter:

Second Quarter:

Third Quarter:

Fourth Quarter:

Alternatively, the 7-day leap week can stand-alone after the 30-day month of December.

Epoch

Provided that years always start on Monday, the Symmetry010 calendar shares the same epoch as the Gregorian calendar, starting on Monday, January 1, 1 AD. This was also the same epoch as that of the Symmetry454 calendar, the ISO calendar, and the Revised Julian calendar. The Symmetry010 year number before the epoch was year zero, to be consistent with the astronomical convention.

Leap Rule

Non-leap (common) years have 52 weeks = 364 days. Leap years, which occur at intervals of 6 or 5 years, have a leap week appended to December, shown above as week 53 of the calendar year = 371 days.

The Symmetry010 calendar employs a superior symmetrical smoothly-spread leap rule that ensures excellent long-term astronomical accuracy:

The simple fixed arithmetic 52/293 leap rule has 52 leap years that are automatically and inherently symmetrically spread as smoothly as possible within each repeating cycle of 293 years:

With 52 leap weeks in the cycle, and 52 weeks in a regular year, the fixed cycle length equals exactly 294 regular years, and the average interval between leap weeks is exactly 294 weeks.

The Symmetry010 calendar mean year ≡ 365+⁷¹/₂₉₃ days ≡ 365 days 5 hours 48 minutes 56+¹⁵²/₂₉₃ seconds. This is intentionally slightly shorter than the present era mean northward equinoctial year of about 365 days 5 hours 49 minutes 0 seconds, ensuring essentially drift-free performance for more than 4 future millennia.

Due to the symmetrical arrangement of leap years, the timing of the mean northward equinox moment always falls at the cycle average in the first year of every 293-year cycle. This feature simplifies astronomical performance evaluations. Click here for more information about symmetrical leap cycles.

Using this leap cycle as described, in the present era the mean northward equinox lands near midnight at the start of Symmetry010 date March 19^th (reference meridian at Jerusalem, Israel).

The Calendar Leap Cycles web page explains why the 52/293 leap rule is preferred and compares it with a wide range of alternative leap rules.

Tweet

Within the original 140-character limit of Twitter.com, the following Tweet defines the rules of the Symmetry010 calendar:

Common year 52 weeks = 30+31+30 days/quarter; append 7 days if remainder of (52×Year+146)/293 < 52; quarters start Monday; epoch Jan 1, 1 AD

Benefits of the Symmetry010 Calendar

• The Symmetry010 calendar is perpetual — a permanent copy can be reused every year.
• It conserves the 7-day week.  There are no intercalated or null or leap days outside of the traditional 7-day weekly cycle.
• Its symmetrical structure paves the way to simpler, aesthetically pleasing calendar designs.
• The symmetrical 52/293 leap rule has excellent long-term calendar drift performance relative to the astronomical mean northward equinox.
• Every Symmetry010 year and quarter starts on Monday and ends on Sunday.
• Its symmetrical 13-week quarters are always identical, having the same number of weekdays and weekend days.
  • In leap years the 4^th quarter has 14 weeks, but this occurs only once per 24 or 20 quarters.
• Every date has permanently fixed week-in-year and day-in-year numbers, facilitating administrative, academic, commercial and industrial applications, and simplifying calendar arithmetic.
• There is always a whole number of weeks in every year (non-leap year = 52 weeks, leap year = 53 weeks) and in every quarter (13 weeks, last quarter of leap year = 14 weeks).
• Every secular holiday, event, anniversary, birthday, and memorial day has a permanently fixed weekday and date, because the calendar is perpetual.
• Holiday and/or special day overlaps are less likely to occur and are easy to predict and avoid.
• Sunday, April 7^th is proposed as a permanently fixed Symmetry010 date for Easter, based on the median date of the Sunday after the day of the astronomical lunar opposition that is on or after the day of the astronomical northward equinox, calculated for the meridian of Jerusalem.
  • Fixing Easter also perpetually fixes all Easter-related ecclesiastical calendar dates (counted before or after Easter).
  • See Appendix: A Declaration of the Second Ecumenical Council of the Vatican on Revision of the Calendar; near the end before the notes of the archived document Constitution on the sacred liturgy Sacrosanctum Concilium solemnly promulgated by His Holiness Pope Paul VI on December 4, 1963.
• The coherent structure of the calendar enables simple arithmetic expressions in calculating the following for statistical or business purposes:  weekday; day number of year, quarter or month; week number of year or quarter;  month number of year or quarter;  weekday.
• Symmetry010 calendar and its arithmetic is in the public domain, allowing royalty-free computer implementation and its free use without copyright restrictions.
• The freely available Kalendis computer program demonstrates the calendar and inter-converts dates.
• Friday the 13^th never happens.

Symmetry010 and Symmetry454 Calendar Documentation

The following documentation is in Adobe Acrobat Portable Document Format (PDF).

All Symmetry010 and Symmetry454 calendar layouts show the calendar for this year and every year, because every year is the same!

Click here to access quick reference manual date conversion sheets.

Come back for updates -- check the version numbers and revision dates, as well as the web site news.

Short File Name and PDF Size	Description (see also the Kalendis freeware program)
Symmetry010 Summary 426 KB	The Symmetry010 calendar has a nearly uniform 30+31+30 days per quarter structure. Introduction to the Symmetry010 Calendar — the Executive Summary: Overview, 3 by 4 month layout, quad puzzle design, and list of benefits.
Symmetry454 Summary 428 KB	For those interested in a slightly more radical calendar design with significant further benefits, the Symmetry454 calendar has a 4+5+4 weeks per quarter structure. Introduction to the Symmetry454 Calendar — the Executive Summary: Overview, 3 by 4 month layout, quad stack design, and list of benefits. Click here to switch to the Symmetry454 calendar home page.
010 Quarter Layout 137 KB	A calendar design depicting the year as a single repeating quarter, shown in portrait and landscape layouts, which could be manufactured as attractive flip calendars.
010 Wide Layout 163 KB	A calendar design stretching each month into a single row across a legal size page in landscape layout, with and without ordinal week and day numbers. These layouts are handy for planning projects and monthly meetings. (Conceptual design by Marc Elliott.)

FAQs 1 MB	Frequently Asked Questions (FAQs) about the Symmetry454 and Symmetry010 calendars.
Holidays & Events 577 KB	Explains how Symmetry010 and Symmetry454 permanently fix birthdays, anniversaries, memorials, holidays, annual events, etc.
Compare 152 KB	A single-page table comparing some properties of the Symmetry010 and Gregorian calendars.
Basic Arithmetic 898 KB	Basic Symmetry454 and Symmetry010 Calendar Arithmetic: This document is for those who want to know how to implement these calendars in computer systems, how to do calendar calculations, how to test for leap years, or how to interconvert dates from and to other calendars.
Convert by Hand 61 KB	Simple instructions for hand-converting any year 1900 to 2099 Gregorian date to Symmetry010, according to the policy that the ISO standard leap rule shall always be used for such conversions because it perpetually maintains a standard relationship to the Gregorian Calendar. (Concept and initial development by Shriramana Sharma of India.)
References 43 KB	Literature and internet references cited by the above documents.
What is Irvember?	A brief and hopefully amusing history of the Leap Week name.

Publicity

• Designs for a new year, in the Innovators section of the Toronto Star newspaper, Friday, December 24, 2004, page A3, by reporter Peter Gorrie.
• Star Trek Math Inspires Calendar Reform, Discovery Channel, Thursday, December 30, 2004, by Jennifer Viegas, Discovery News.
• Time and Again, the Calendar Comes Up Short: Sticklers for Symmetry Lament Imperfections in the 400-Year-Old Gregorian System; Earth’s Inconvenient Orbit, The Wall Street Journal, December 31, 2009, by Charles Forelle, The Numbers Guy.
• New Year’s Revolution: A proposed new calendar would give February an extra week and start every month on a Monday, University of Toronto Magazine, in Leading Edge, Winter 2011, by Scott Anderson.

This page updated May 5, 2020 (Symmetry454) = May 3, 2020 (Symmetry010) = May 1, 2020 (Gregorian)