Nineteen months of nineteen

A calendar that squares the year — nineteen months of nineteen days, a festival parked outside time, and a new year that waits for the equinox in Tehran. The Badíʿ calendar, running since 1844. ← Calendar Contraptions

Most calendars patch a mismatch: a moon that won't fit the sun, weeks that won't fit anything. The Badíʿ calendar — the calendar of the Baháʼí Faith, drawn up by its founder-figure the Báb in the 1840s — sidesteps the moon entirely. It takes the number nineteen, which the Báb's numerology held sacred and which the solar year happens to favour too (√365.2422 ≈ 19.11, the closest a whole number comes to the square root of the year), and builds a square: nineteen months of nineteen days. Nineteen squared is 361. The four or five days needed to close the gap to a real year are not part of any month — they are Ayyám-i-Há, the Days of Há, parked between the eighteenth and nineteenth months, outside the calendar's arithmetic altogether. The year count is young: year 1 began at sunset in March 1844, so this calendar is younger than the bicycle.

Pick a date. The machine reads it back the way a Badíʿ calendar page would — and then shows the machinery that decides when each year actually begins.

Nineteen, nineteen times

Nothing in this calendar has a variable length until the very end. Nineteen months, every one nineteen days. The days of the month carry the same nineteen names as the months themselves: the ninth day of every single month is Asmáʼ (Names), the ninth month. The Báb took the names from the Duʻáy-i-Sahar, a dawn prayer for Ramadan by the fifth Shia Imam, Muhammad al-Baqir — each one an attribute of God: Splendour, Glory, Beauty, Grandeur, Light, Mercy, Words, Perfection, Names, Might, Will, Knowledge, Power, Speech, Questions, Honour, Sovereignty, Dominion, Loftiness. In his Persian Bayán he grouped the months four ways — three months of fire, four of air, six of water, six of earth. The only moving part in the whole year is the seam between month eighteen (Mulk, Dominion) and month nineteen (ʻAláʼ, Loftiness, the month of fasting): the four or five days that square the arithmetic away into a true solar year.

The days outside time

The intercalary days got a name with a numerology joke folded in: Ayyám-i-Há, "the Days of Há" — Há being the Arabic letter whose abjad numeral is 5, the most days the festival can ever run. Baháʼu'lláh, who confirmed the calendar in his book of laws, the Kitáb-i-Aqdas (1873), placed the days here himself — immediately before the fasting month — and devoted them to hospitality, gift-giving and charity. The move was a clean break from Islam: the Qurʼan forbids intercalation outright ("adjusting the sacred months" is named as an act of disbelief), and the Báb answered by parking the extra days outside the months entirely — a festival of days that belong to no month at all. (The Islamic calendar instead let its year wander the seasons — that story is in The year that wanders.) The Oxford Companion to the Year even files a scholarly quibble about it: of Ayyám-i-Há's five days, four are "epagomenal" days that square the count and only the fifth is intercalary in the strict sense. The festival's own answer is simpler: all of them are outside time.

The wheel of cycles

Nineteen years make a Váḥid ("Unity" — the abjad value of the word is 19), and every year of the cycle has its own name, from Alif to Váḥid. Nineteen Váḥids make a Kull-i-Shayʼ — "All Things", 361 years, nineteen squared again. The first Kull-i-Shayʼ of the era runs from 1844 to 2204: the tenth Váḥid began at Naw-Rúz 2015, the eleventh opens in 2034, and the wheel turns over completely in 2205. (A nineteen-year cycle of years is an old idea — Meton drew one for Athens in 432 BC — but Meton's circle reconciles moon and sun, while this one squares the year against itself.)

The waiting machine

An equinox is an instant, not a day — and a Baháʼí day runs from sunset to sunset. So the new year needed a rule, a place and a verdict. The rule came from Baháʼu'lláh (Naw-Rúz is the day the sun enters Aries), but the place was left deliberately open for a century and a half. On 10 July 2014 the Universal House of Justice — the elected body Baháʼís regard as their governing council — chose Tehran, the birthplace of Baháʼu'lláh, and fixed the definition: Naw-Rúz is the sunset-to-sunset day in Tehran that contains the moment of the March equinox, computed years in advance from astronomical tables (the UK Nautical Almanac Office supplies the data). The same letter unlocked the calendar from the Gregorian: from Naw-Rúz 2015 — year 172, the first year of the tenth Váḥid — the calendar runs on its own astronomy. Before that, the year had simply started at sunset on 20 March every Gregorian year, with Ayyám-i-Há always spanning 26 February – 1 March so it swallowed the Gregorian leap day automatically. The machine below reads the equinox, reads the sunsets, and gives the verdict — including how close some years come to a coin flip.

The fixed dates of the year

Once Naw-Rúz is placed, the year's commemorations follow it like cars on a train — fixed in the Badíʿ year, wandering a day or two on the Gregorian one:

Convert the other way

A brief history of the square

The Báb announced his movement in 1844 — the year the calendar counts from — and set out its machinery in the Kitábu'l-Asmáʼ and the Persian Bayán (5:3). The early version already ran on nineteen-day months, but it began the year at the Persian Nowruz and placed the intercalary days differently. Baháʼu'lláh, the figure the Báb's writings pointed toward, confirmed the calendar and settled it: Naw-Rúz as the first day of the year, Ayyám-i-Há immediately before the last month, and the new year defined as the day "on which the sun passes into the constellation Aries" — interpreted as the vernal equinox, with the question of where to take it from left open. Around 1870 he had Nabíl-i-Aʻzam, author of The Dawn-Breakers, write up the calendar's rules. The West implemented the calendar in 1907. And in 2014 the Universal House of Justice closed the open question with Tehran, published fifty years of dates computed from HM Nautical Almanac Office data (with Tehran's position fixed in the WGS84 system), and started the common era at sunset on 20 March 2015.

Days begin at sunset, as in Judaism and Islam, so every date here owns its preceding evening too. The week runs from Jalál (Glory, Saturday) to Istiqlál (Independence, Friday) — Baháʼí writings make Friday the day of rest, though the practice is not kept everywhere; the UK's Baháʼí community has confirmed it does not currently keep it. The weekday names are the same attribute-of-God vocabulary as the months and the days of the month.

Where it cheats

Not in its lengths — the months are perfect squares all year. The honest seams are about when the year starts. The pre-2015 years ran on Gregorian rails: Naw-Rúz every 21 March, whether or not the sky agreed (this page's astronomy would have put the equinox before a Tehran sunset on 20 March — implying a 20 March Naw-Rúz — in 51 of the 171 locked years; the rule pinned them all at the 21st anyway). From 2015 the calendar follows the sky, which means it also inherits the sky's close calls: in 2026 the equinox missed the deciding Tehran sunset by 49 seconds — the tightest call of the whole era, which is why the published table (computed with the Nautical Almanac's data) is the authority here; this page's own astronomy lands the other side of that sunset, and it defers. After 2026 the next-tightest calls in the next two centuries are 2059 (about two and a half minutes) and 2191 (about twelve); the era's first 19-March Naw-Rúz, by this page's astronomy, arrives in 2096. And past 2065 the published table runs out — later Naw-Rúz dates are published in advance from fresh astronomical tables, so this page computes them itself and flags the years. A calendar that starts the year at a sunset is, eventually, a calendar decided at the horizon.